dev: Integrates glog/gflags with FetchContent style.

[innerNULL]

hi, just a little update, but maybe this can make the installation be more convenient : )

[innerNULL]

Running tests...
Test project /workspace/qmf/build
      Start  1: BPREngineTest
 1/69 Test  #1: BPREngineTest ....................   Passed    0.21 sec
      Start  2: DatasetReaderTest
 2/69 Test  #2: DatasetReaderTest ................   Passed    0.00 sec
      Start  3: EngineTest
 3/69 Test  #3: EngineTest .......................   Passed    0.00 sec
      Start  4: FactorDataTest
 4/69 Test  #4: FactorDataTest ...................   Passed    0.00 sec
      Start  5: MatrixTest
 5/69 Test  #5: MatrixTest .......................   Passed    0.00 sec
      Start  6: MetricsTest
 6/69 Test  #6: MetricsTest ......................   Passed    0.00 sec
      Start  7: MetricsManagerTest
 7/69 Test  #7: MetricsManagerTest ...............   Passed    0.00 sec
      Start  8: ParallelExecutorTest
 8/69 Test  #8: ParallelExecutorTest .............   Passed    0.00 sec
      Start  9: ThreadPoolTest
 9/69 Test  #9: ThreadPoolTest ...................   Passed    0.00 sec
      Start 10: UtilTest
10/69 Test #10: UtilTest .........................   Passed    0.00 sec
      Start 11: VectorTest
11/69 Test #11: VectorTest .......................   Passed    0.00 sec
      Start 12: WALSEngineTest
12/69 Test #12: WALSEngineTest ...................   Passed    0.01 sec
      Start 13: demangle
13/69 Test #13: demangle .........................   Passed    0.00 sec
      Start 14: logging
14/69 Test #14: logging ..........................   Passed    0.38 sec
      Start 15: signalhandler
15/69 Test #15: signalhandler ....................   Passed    0.00 sec
      Start 16: stacktrace
16/69 Test #16: stacktrace .......................   Passed    0.00 sec
      Start 17: stl_logging
17/69 Test #17: stl_logging ......................   Passed    0.00 sec
      Start 18: symbolize
18/69 Test #18: symbolize ........................   Passed    0.00 sec
      Start 19: strip_flags_help
19/69 Test #19: strip_flags_help .................   Passed    0.01 sec
      Start 20: unittest
20/69 Test #20: unittest .........................   Passed    0.01 sec
      Start 21: help-reporting
21/69 Test #21: help-reporting ...................   Passed    0.01 sec
      Start 22: long-helpstring
22/69 Test #22: long-helpstring ..................   Passed    0.01 sec
      Start 23: changed_bool1
23/69 Test #23: changed_bool1 ....................   Passed    0.01 sec
      Start 24: changed_bool2
24/69 Test #24: changed_bool2 ....................   Passed    0.01 sec
      Start 25: changeable_string_var
25/69 Test #25: changeable_string_var ............   Passed    0.01 sec
      Start 26: nohelp
26/69 Test #26: nohelp ...........................   Passed    0.01 sec
      Start 27: help=false
27/69 Test #27: help=false .......................   Passed    0.01 sec
      Start 28: helpfull
28/69 Test #28: helpfull .........................   Passed    0.01 sec
      Start 29: helpshort
29/69 Test #29: helpshort ........................   Passed    0.01 sec
      Start 30: helpshort-tldflag1
30/69 Test #30: helpshort-tldflag1 ...............   Passed    0.01 sec
      Start 31: helpshort-tldflag2
31/69 Test #31: helpshort-tldflag2 ...............   Passed    0.01 sec
      Start 32: helpshort-main
32/69 Test #32: helpshort-main ...................   Passed    0.01 sec
      Start 33: helpshort_main
33/69 Test #33: helpshort_main ...................   Passed    0.01 sec
      Start 34: helpon
34/69 Test #34: helpon ...........................   Passed    0.01 sec
      Start 35: helpon=gflags
35/69 Test #35: helpon=gflags ....................   Passed    0.01 sec
      Start 36: helpon_gflags
36/69 Test #36: helpon_gflags ....................   Passed    0.01 sec
      Start 37: helpon=gflags_unittest
37/69 Test #37: helpon=gflags_unittest ...........   Passed    0.01 sec
      Start 38: helpmatch_reporting
38/69 Test #38: helpmatch_reporting ..............   Passed    0.01 sec
      Start 39: helpmatch=unittest
39/69 Test #39: helpmatch=unittest ...............   Passed    0.01 sec
      Start 40: helpmatch=nosuchsubstring
40/69 Test #40: helpmatch=nosuchsubstring ........   Passed    0.01 sec
      Start 41: helpon=nosuchmodule
41/69 Test #41: helpon=nosuchmodule ..............   Passed    0.01 sec
      Start 42: helppackage
42/69 Test #42: helppackage ......................   Passed    0.01 sec
      Start 43: helpxml
43/69 Test #43: helpxml ..........................   Passed    0.01 sec
      Start 44: version-1
44/69 Test #44: version-1 ........................   Passed    0.01 sec
      Start 45: version-2
45/69 Test #45: version-2 ........................   Passed    0.01 sec
      Start 46: undefok-1
46/69 Test #46: undefok-1 ........................   Passed    0.01 sec
      Start 47: undefok-2
47/69 Test #47: undefok-2 ........................   Passed    0.01 sec
      Start 48: undefok-3
48/69 Test #48: undefok-3 ........................   Passed    0.01 sec
      Start 49: undefok-4
49/69 Test #49: undefok-4 ........................   Passed    0.01 sec
      Start 50: undefok-5
50/69 Test #50: undefok-5 ........................   Passed    0.01 sec
      Start 51: undefok-6
51/69 Test #51: undefok-6 ........................   Passed    0.01 sec
      Start 52: flagfile.1
52/69 Test #52: flagfile.1 .......................   Passed    0.01 sec
      Start 53: flagfile.2
53/69 Test #53: flagfile.2 .......................   Passed    0.01 sec
      Start 54: flagfile.3
54/69 Test #54: flagfile.3 .......................   Passed    0.01 sec
      Start 55: fromenv=version
55/69 Test #55: fromenv=version ..................   Passed    0.01 sec
      Start 56: tryfromenv=version
56/69 Test #56: tryfromenv=version ...............   Passed    0.01 sec
      Start 57: fromenv=help
57/69 Test #57: fromenv=help .....................   Passed    0.01 sec
      Start 58: tryfromenv=help
58/69 Test #58: tryfromenv=help ..................   Passed    0.01 sec
      Start 59: fromenv=helpfull
59/69 Test #59: fromenv=helpfull .................   Passed    0.01 sec
      Start 60: tryfromenv=helpfull
60/69 Test #60: tryfromenv=helpfull ..............   Passed    0.01 sec
      Start 61: tryfromenv=undefok
61/69 Test #61: tryfromenv=undefok ...............   Passed    0.01 sec
      Start 62: tryfromenv=weirdo
62/69 Test #62: tryfromenv=weirdo ................   Passed    0.01 sec
      Start 63: tryfromenv-multiple
63/69 Test #63: tryfromenv-multiple ..............   Passed    0.01 sec
      Start 64: fromenv=test_bool
64/69 Test #64: fromenv=test_bool ................   Passed    0.01 sec
      Start 65: fromenv=test_bool-ok
65/69 Test #65: fromenv=test_bool-ok .............   Passed    0.01 sec
      Start 66: version-overrides-fromenv
66/69 Test #66: version-overrides-fromenv ........   Passed    0.01 sec
      Start 67: dashdash
67/69 Test #67: dashdash .........................   Passed    0.01 sec
      Start 68: always_fail
68/69 Test #68: always_fail ......................   Passed    0.01 sec
      Start 69: gflags_declare
69/69 Test #69: gflags_declare ...................   Passed    0.00 sec

100% tests passed, 0 tests failed out of 69