[llvm] [LLVM] Change error messages to start with lower case (PR #113748)

[Matt Arsenault via llvm-commits]

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@@ -156,7 +156,7 @@ int TGLexer::getNextChar() {
       return EOF;
     }
     PrintError(getLoc(),
-               "NUL character is invalid in source; treated as space");
+               "nul character is invalid in source; treated as space");
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arsenm wrote:

Seems like a special case to leave as is 

https://github.com/llvm/llvm-project/pull/113748