Pass through even more LIBCXX_* variables to libfuzzer's custom lib++

Similar to D120946, pass LIBCXX_HAS_GCC_S_LIB and LIBCXX_USE_COMPILER_RT
through to the custom lib++ builds so that libfuzzer doesn't end up with
a .deplibs section that links against those libraries when the
variables are set to false.

Reviewed By: phosek

Differential Revision: https://reviews.llvm.org/D127912

compiler-rt/cmake/Modules/AddCompilerRT.cmake

@@ -646,8 +646,10 @@ macro(add_custom_libcxx name prefix)
     CMAKE_READELF
     CMAKE_SYSROOT
     LIBCXX_HAS_MUSL_LIBC
+    LIBCXX_HAS_GCC_S_LIB
     LIBCXX_HAS_PTHREAD_LIB
     LIBCXX_HAS_RT_LIB
+    LIBCXX_USE_COMPILER_RT
     LIBCXXABI_HAS_PTHREAD_LIB
     PYTHON_EXECUTABLE
     Python3_EXECUTABLE