Revert "Set the default C standard to C99 when targeting the PS4."

This reverts r265359.

It breaks
- llvm-clang-lld-x86_64-scei-ps4-ubuntu-fast
- llvm-clang-lld-x86_64-scei-ps4-windows10pro-fast

Failing Tests (5):
    Clang :: FixIt/fixit-errors.c
    Clang :: Preprocessor/init.c
    Clang :: Sema/attr-deprecated.c
    Clang :: Sema/nullability.c
    Clang :: SemaObjC/objcbridge-attribute-arc.m

llvm-svn: 265601