add support for ugly *64 functions with _LARGEFILE64_SOURCE

musl does not support legacy 32-bit-off_t whatsoever. off_t is always
64 bit, and correct programs that use off_t and the standard functions
will just work out of the box. (on glibc, they would require
-D_FILE_OFFSET_BITS=64 to work.) however, some programs instead define
_LARGEFILE64_SOURCE and use alternate versions of all the standard
types and functions with "64" appended to their names.

we do not want code to actually get linked against these functions
(it's ugly and inconsistent), so macros are used instead of prototypes
with weak aliases in the library itself. eventually the weak aliases
may be added at the library level for the sake of using code that was
originally built against glibc, but the macros will still be the
desired solution in the headers.

include/stdio.h

@@ -167,6 +167,18 @@ char *fgets_unlocked(char *, int, FILE *);
 int fputs_unlocked(const char *, FILE *);
 #endif
 
+#ifdef _LARGEFILE64_SOURCE
+#define tmpfile64 tmpfile
+#define fopen64 fopen
+#define freopen64 freopen
+#define fseeko64 fseeko
+#define ftello64 ftello
+#define fgetpos64 fgetpos
+#define fsetpos64 fsetpos
+#define fpos64_t fpos_t
+#define off64_t off_t
+#endif
+
 #ifdef __cplusplus
 }
 #endif