[libfuzzer] Fix -runs=X flaky test (fuzzer-finalstats.test) (#96914)

Disables LSan in order to remove a 1% flake rate in this test.
There's some logic in LeakSanitizer and its integration into libFuzzer
that will disable LSan and re-run the input. This only happens when more
malloc()s are detected than free()s. Under high system load, this
appears to be possible as the "more mallocs than frees" is dependent on
walltime. In these instances, the number of runs ends up being `n + 1`,
which is undesirable.

compiler-rt/test/fuzzer/fuzzer-finalstats.test

@@ -2,14 +2,22 @@
 UNSUPPORTED: target={{.*}}
 
 RUN: %cpp_compiler %S/SimpleTest.cpp -o %t-SimpleTest
-RUN: %run %t-SimpleTest -seed=1 -runs=77 -print_final_stats=1 2>&1 | FileCheck %s --check-prefix=FINAL_STATS
+
+// Note: `-detect_leaks=0` is required to prevent flakiness in this test.
+// There's some logic in LeakSanitizer and its integration into libFuzzer that
+// will disable LSan and re-run the input. This only happens when more malloc()s
+// are detected than free()s. Under high system load, this appears to be
+// possible as the "more mallocs than frees" is dependent on walltime. In these
+// instances, the number of runs ends up being `n + 1`, which is undesirable.
+
+RUN: %run %t-SimpleTest -seed=1 -runs=77 -print_final_stats=1 -detect_leaks=0 2>&1 | FileCheck %s --check-prefix=FINAL_STATS
 FINAL_STATS: stat::number_of_executed_units: 77
 FINAL_STATS: stat::average_exec_per_sec:     0
 FINAL_STATS: stat::new_units_added:
 FINAL_STATS: stat::slowest_unit_time_sec:    0
 FINAL_STATS: stat::peak_rss_mb:
 
-RUN: %run %t-SimpleTest %S/dict1.txt -runs=33 -print_final_stats=1 2>&1 | FileCheck %s --check-prefix=FINAL_STATS1
+RUN: %run %t-SimpleTest %S/dict1.txt -runs=33 -print_final_stats=1 -detect_leaks=0 2>&1 | FileCheck %s --check-prefix=FINAL_STATS1
 FINAL_STATS1: stat::number_of_executed_units: 33
 FINAL_STATS1: stat::peak_rss_mb: