Replace pragma onces with guards because preproc names are useful

standalone_libraries/regex.h

@@ -1,4 +1,5 @@
-#pragma once
+#ifndef FIRST_REGEX_HEADER
+#define FIRST_REGEX_HEADER
 #include <stdint.h>
 #include <stdbool.h>
 
@@ -91,3 +92,4 @@ RE_API RE_Match RE3_FindAgain(RE_Regex *regex, char *string, RE_Int len, RE_Matc
 RE_API RE_Int RE3_MatchFront(RE_Regex *regex, char *string, RE_Int len, char *string_front);
 RE_API RE_Regex *RE1_Parse(char *buff, RE_Int buffsize, char *string);
 RE_API RE_Regex *RE2_Parse(char *buff, RE_Int buffsize, char *string, RE_Int len);
+#endif