Respect cmake link flags when compiling test files

[fjricci]

Summary

Makes sure that calls to try_compile run with user-supplied
additional linker flags

[fjricci]

Fix commit message

[beanz]

This patch looks fine to me, however I'd like to see the resolution on D31098 before landing this. If we change the CMake policy CMP0056 to NEW, I think that will automatically address this issue resulting in us not needing this patch.

[fjricci]

Yep, that patch does appear to fix my issue in its current form. I'll abandon this, with the assumption that will go in.

cmake/Modules/CompilerRTDarwinUtils.cmake

function(darwin_test_archs os valid_archs)
   # a valid or useful architecture for the iOS simulator we should drop it.
   if(${os} MATCHES "^(iossim|tvossim|watchossim)$")
     list(REMOVE_ITEM archs "x86_64h")
   endif()
 
   set(working_archs)
   foreach(arch ${archs})
    
-    set(arch_linker_flags "-arch ${arch} ${os_linker_flags}")
+    set(arch_linker_flags "-arch ${arch} ${os_linker_flags} ${CMAKE_EXE_LINKER_FLAGS}")
     if(TEST_COMPILE_ONLY)
       try_compile_only(CAN_TARGET_${os}_${arch} -v -arch ${arch} ${DARWIN_${os}_CFLAGS})
     else()
       try_compile(CAN_TARGET_${os}_${arch} ${CMAKE_BINARY_DIR} ${SIMPLE_C}
                   COMPILE_DEFINITIONS "-v -arch ${arch}" ${DARWIN_${os}_CFLAGS}
                   CMAKE_FLAGS "-DCMAKE_EXE_LINKER_FLAGS=${arch_linker_flags}"
                   OUTPUT_VARIABLE TEST_OUTPUT)
     endif()