test_fallback_malloc.pass.cpp fails on Linux

Hi,

Looks like this test needs to link to gcc_s :

******************** TEST 'libc++abi :: test_fallback_malloc.pass.cpp'
FAILED ********************
Command: ['/havana/dist/llvm/bin/clang++', '-o',
'/havana/src/llvm/build/lib/test/Output/test_fallback_malloc.pass.cpp.exe',
'/
havana/src/llvm/build/lib/test/Output/test_fallback_malloc.pass.cpp.o',
'-v', '-nodefaultlibs', '-L/havana/src/llvm/build/lib',
'-Wl,-rpath,/havana/src/llvm/build/lib',
'-L/havana/src/llvm/build/lib',
'-Wl,-rpath,/havana/src/llvm/build/lib', '-lc++', '-l
c++abi', '-lc', '-lm', '-lpthread', '-lrt', '-lunwind', '-ldl']
Exit Code: 1
Standard Error:

Would be better to use compiler-rt when using libunwind (so we don’t link two unwinders), but it should be fine to link libgcc as long as it comes after libunwind.