Adapt help string to what the code is doing (default is lang_gnu99). Thanks rdivacky!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@65689 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/Driver/clang.cpp b/Driver/clang.cpp
index 6fdd18a..3e7b9cd 100644
--- a/Driver/clang.cpp
+++ b/Driver/clang.cpp
@@ -433,9 +433,9 @@
                    clEnumValN(lang_c99,      "iso9899:1999",   "ISO C 1999"),
 //                 clEnumValN(lang_c99,      "iso9899:199x",   "ISO C 1999"),
                    clEnumValN(lang_gnu89,    "gnu89",
-                              "ISO C 1990 with GNU extensions (default for C)"),
+                              "ISO C 1990 with GNU extensions"),
                    clEnumValN(lang_gnu99,    "gnu99",
-                              "ISO C 1999 with GNU extensions"),
+                              "ISO C 1999 with GNU extensions (default for C)"),
                    clEnumValN(lang_gnu99,    "gnu9x",
                               "ISO C 1999 with GNU extensions"),
                    clEnumValN(lang_cxx98,    "c++98",