CMAKE_CXX_COMPILER_ARG1
When `-DCMAKE_CXX_COMPILER='clang++;-stdlib=libc++;-m32'` is provided, `-stdlib=libc++ -m32` flags are printed in the summary now.
APPEND_{CPP,C,CXX,LD}FLAGS
The content of those variables is appended to the each target after the flags added by the build system.