[profile] Build with -fms-extensions in MinGW mode

54902e00 added a use of
/alternatename via a #pragma comment(linker); in MinGW mode, this
requires building with -fms-extensions. (This flag is added to
SANITIZER_COMMON_CFLAGS in the toplevel CMakeLists.txt.)

This avoids a warning when building in MinGW mode (about an unknown
pragma being ignored), and presumably also makes the code work as
intended.

Differential Revision: https://reviews.llvm.org/D107620