Change default C dialect for PS5 to gnu17/gnu18.

[probinson]

LGTM

clang/lib/Basic/LangStandards.cpp

case Language::OpenCLCXX:
     return LangStandard::lang_openclcpp10;
   case Language::CUDA:
     return LangStandard::lang_cuda;
   case Language::Asm:
   case Language::C:
     if (CLANG_DEFAULT_STD_C != LangStandard::lang_unspecified)
       return CLANG_DEFAULT_STD_C;
 
-    // The PS4 and PS5 use C99 as the default C standard.
-    if (T.isPS())
+    // The PS4 uses C99 as the default C standard.
+    if (T.isPS4())
       return LangStandard::lang_gnu99;
     return LangStandard::lang_gnu17;
   case Language::ObjC:
     if (CLANG_DEFAULT_STD_C != LangStandard::lang_unspecified)
       return CLANG_DEFAULT_STD_C;
 
     return LangStandard::lang_gnu11;
   case Language::CXX:

clang/test/Preprocessor/init.c

 // PS4:#define __SIZEOF_WCHAR_T__ 2
 // PS4:#define __SIZEOF_WINT_T__ 4
 // PS4:#define __SIZE_TYPE__ long unsigned int
 // PS4:#define __SIZE_WIDTH__ 64
 // PS4:#define __SSE2_MATH__ 1
 // PS4:#define __SSE2__ 1
 // PS4:#define __SSE_MATH__ 1
 // PS4:#define __SSE__ 1
-// PS4:#define __STDC_VERSION__ 199901L
+// PS4ONLY:#define __STDC_VERSION__ 199901L
+// PS5ONLY:#define __STDC_VERSION__ 201710L
 // PS4:#define __UINTMAX_TYPE__ long unsigned int
 // PS4:#define __USER_LABEL_PREFIX__
 // PS4:#define __WCHAR_MAX__ 65535
 // PS4:#define __WCHAR_TYPE__ unsigned short
 // PS4:#define __WCHAR_UNSIGNED__ 1
 // PS4:#define __WCHAR_WIDTH__ 16
 // PS4:#define __WINT_TYPE__ int
 // PS4:#define __WINT_WIDTH__ 32