-Wc++98-compat warnings for the lexer.

This also adds a -Wc++98-compat-pedantic for warning on constructs which would
be diagnosed by -std=c++98 -pedantic (that is, it warns even on C++11 features
which we enable by default, with no warning, in C++98 mode).


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@142034 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Lex/PPMacroExpansion.cpp b/lib/Lex/PPMacroExpansion.cpp
index 9b20605..e10c95c 100644
--- a/lib/Lex/PPMacroExpansion.cpp
+++ b/lib/Lex/PPMacroExpansion.cpp
@@ -421,8 +421,10 @@
 
     // Empty arguments are standard in C99 and C++0x, and are supported as an extension in
     // other modes.
-    if (ArgTokens.size() == ArgTokenStart && !Features.C99 && !Features.CPlusPlus0x)
-      Diag(Tok, diag::ext_empty_fnmacro_arg);
+    if (ArgTokens.size() == ArgTokenStart && !Features.C99)
+      Diag(Tok, Features.CPlusPlus0x ?
+           diag::warn_cxx98_compat_empty_fnmacro_arg :
+           diag::ext_empty_fnmacro_arg);
 
     // Add a marker EOF token to the end of the token list for this argument.
     Token EOFTok;