Correctly type the global char arrays in build.h as const (#1827)

Given that these arrays are typed as const in in build.c
(and in OOT's include/build.h), it seems logical to also type them as
const here.

include/build.h

@@ -1,8 +1,8 @@
 #ifndef BUILD_H
 #define BUILD_H
 
-extern char gBuildCreator[];
-extern char gBuildDate[];
-extern char gBuildMakeOption[];
+extern const char gBuildCreator[];
+extern const char gBuildDate[];
+extern const char gBuildMakeOption[];
 
 #endif

src/boot/build.c

@@ -1,3 +1,5 @@
+#include "build.h"
+
 const char gBuildCreator[] = "zelda@srd44";
 const char gBuildDate[] = "00-07-31 17:04:16";
 const char gBuildMakeOption[] = "";