Fixed warnings about deprecated conversion from string constant to char*. Submitted by timeless.

src/compiler/glslang.l

@@ -318,7 +318,7 @@ int PaParseStrings(char* argv[], int strLen[], int argc, TParseContext& parseCon
         return 0;
 }
 
-void yyerror(char *s) 
+void yyerror(const char *s) 
 {
     if (((TParseContext *)cpp->pC)->AfterEOF) {
         if (cpp->tokensBeforeEOF == 1) {

src/compiler/glslang.y

@@ -38,7 +38,7 @@ compiler/tools. Remove it when we can exclusively use the newer version.
 #define parseContext ((TParseContext*)(parseContextLocal))
 #define YYLEX_PARAM parseContextLocal
 #define YY_DECL int yylex(YYSTYPE* pyylval, void* parseContextLocal)
-extern void yyerror(char*);
+extern void yyerror(const char*);
 
 #define FRAG_VERT_ONLY(S, L) {                                                  \
     if (parseContext->language != EShLangFragment &&                             \