[Runner] Push /opt/${target}/${target}/lib{,64} to linker search path

When compiling with GCC this makes sure its libraries have precedence over
anything else, in particular other compiler libraries that may be elsewhere, for
example `CompilerSupportLibraries_jll` used as dependency during the build.

src/Runner.jl

@@ -348,6 +348,15 @@ function generate_compiler_wrappers!(platform::AbstractPlatform; bin_path::Abstr
     end
 
     function gcc_compile_flags!(p::AbstractPlatform, flags::Vector{String} = String[])
+        if Sys.islinux(p) || Sys.isfreebsd(p)
+            # Help GCC find its own libraries under `/opt/${target}/${target}/lib{,64}`.
+            # Note: we need to push them directly in the wrappers before any additional
+            # arguments because we want this path to have precedence over anything else.  In
+            # this way for example we avoid libraries from `CompilerSupportLibraries_jll` in
+            # `${libdir}` are picked up by mistake.
+            dir = "/opt/$(aatriplet(p))/$(aatriplet(p))/lib" * (nbits(p) == 32 ? "" : "64")
+            append!(flags, ("-L$(dir)", "-Wl,-rpath-link,$(dir)"))
+        end
         if lock_microarchitecture
             append!(flags, get_march_flags(arch(p), march(p), "gcc"))
         end

test/runners.jl

@@ -128,6 +128,41 @@ end
                 @test endswith(readchomp(iobuff), "Hello World!")
             end
 
+            @testset "C++ - $(platform)" for platform in platforms
+                ur = preferred_runner()(dir; platform=platform)
+                iobuff = IOBuffer()
+                test_c = """
+                #include <iostream>
+                class breakCCompiler; // Courtesy of Meson
+                int main() {
+                    std::cout << "Hello World!" << std::endl;
+                    return 0;
+                }
+                """
+                test_script = """
+                set -e
+                # Install `CompilerSupportLibraries_jll` v0.5.0 in the `\${prefix}` to make
+                # sure it doesn't break compilation of the program
+                mkdir -p \${prefix}
+                wget -qO - "https://github.com/JuliaBinaryWrappers/CompilerSupportLibraries_jll.jl/releases/download/CompilerSupportLibraries-v0.5.0%2B0/CompilerSupportLibraries.v0.5.0.\${target}-libgfortran3.tar.gz" | tar xzf - -C \${prefix}
+                echo '$(test_c)' > test.cpp
+                # Make sure we can compile successfully also when `\${libdir}` is in the
+                # linker search path
+                g++ -o test test.cpp -L\${libdir}
+                ./test
+                """
+                cmd = `/bin/bash -c "$(test_script)"`
+                if arch(platform) == "i686" && libc(platform) == "musl"
+                    # We can't run C++ programs for this platform
+                    @test_broken run(ur, cmd, iobuff; tee_stream=devnull)
+                else
+                    @test run(ur, cmd, iobuff; tee_stream=devnull)
+                    seekstart(iobuff)
+                    # Test that we get the output we expect
+                    @test endswith(readchomp(iobuff), "Hello World!")
+                end
+            end
+
             # This tests that compilers for all Intel Linux platforms can build a simple
             # Fortran program that we can also run
             @testset "Fortran - $(platform)" for platform in filter(p -> Sys.islinux(p) && proc_family(p) == "intel", supported_platforms())
@@ -140,6 +175,7 @@ end
                 """
                 cmd = `/bin/bash -c "echo '$(test_f)' > test.f && gfortran -o test test.f && ./test"`
                 if arch(platform) == "i686" && libc(platform) == "musl"
+                    # We can't run Fortran programs for this platform
                     @test_broken run(ur, cmd, iobuff; tee_stream=devnull)
                 else
                     @test run(ur, cmd, iobuff; tee_stream=devnull)