[GTest][c++17] Silence warnings when building GTest with gcc-toolset-12

This change fixes a build break introduced by aafad2d2(#70353) on
the clang-ppc64le-rhel build bot. If the third-party Google Test suite
is built using gcc-toolset-12, the implementation of std::stable_sort in
the toolchain will use a get_temporary_buffer declaration that is marked
_GLIBCXX17_DEPRECATED. This change adds -Wno-deprecated-declarations to
the GTest flags if the toolchain is detected in the build compiler on linux.