glsl: replace _strtoui64() with strtoull() for MSVC

Now that MSVC 2013 is required we can remove this.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>

src/compiler/glsl/glsl_lexer.ll

@@ -113,11 +113,7 @@ literal_integer(char *text, int len, struct _mesa_glsl_parse_state *state,
    if (base == 16)
       digits += 2;
 
-#ifdef _MSC_VER
-   unsigned __int64 value = _strtoui64(digits, NULL, base);
-#else
    unsigned long long value = strtoull(digits, NULL, base);
-#endif
 
    lval->n = (int)value;