How does Clion use the class library of GCC under Mac?

how does Clion use GCC"s class library under Mac?
I use mac, 10.12 (16A323) and install GCC, using homebrew. There is no problem typing gcc-4.9 on the command line

lyzdeMacBook-Pro-3:~ lyz$ gcc-4.9 -v
Using built-in specs.
COLLECT_GCC=gcc-4.9
COLLECT_LTO_WRAPPER=/usr/local/Cellar/gcc@4.9/4.9.4_1/libexec/gcc/x86_64-apple-darwin16.0.0/4.9.4/lto-wrapper
Target: x86_64-apple-darwin16.0.0
Configured with: ../configure --build=x86_64-apple-darwin16.0.0 --prefix=/usr/local/Cellar/gcc@4.9/4.9.4_1 --libdir=/usr/local/Cellar/gcc@4.9/4.9.4_1/lib/gcc/4.9 --enable-languages=c,cPP,fortran,java,objc,obj-cPP --program-suffix=-4.9 --with-system-zlib --enable-libstdcxx-time=yes --enable-stage1-checking --enable-checking=release --enable-lto --enable-plugin --with-build-config=bootstrap-debug --disable-werror --with-pkgversion="Homebrew GCC 4.9.4_1 --with-all-languages" --with-bugurl=https://github.com/Homebrew/homebrew-core/issues MAKEINFO=missing --disable-nls --with-ecj-jar=/usr/local/opt/ecj/share/java/ecj.jar --enable-multilib
Thread model: posix
gcc version 4.9.4 (Homebrew GCC 4.9.4_1 --with-all-languages)

then I configured GCC"s toolsChain and CMake in CLion according to the online tutorials

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