romdata: include <errno.h> after ultra64.h (fixes the Linux build on macos)

#88 added <errno.h> to the POSIX include block, ahead of ultra64.h.
glibc defines errno as a macro, (*__errno_location ()), which rewrites
the N64 `u8 errno;` fields in PR/os.h (OSContStatus, OSContPad,
OSContRamIo) and fails with "field '__errno_location' declared as a
function". Include it after ultra64.h/bondtypes.h instead. Nothing in
this file reads those struct fields; errno is only read by the mmap
failure diagnostic. No change on Windows.

port/src/romdata.c

@@ -35,8 +35,7 @@ extern int snprintf(char *str, size_t maxsize, const char *format, ...);
 #else
   /* POSIX: mmap the ROM at the fixed cart address (mirrors the VirtualAlloc
    * path). <sys/mman.h> is a host header the decomp include path does not
-   * shadow. */
-  #include <errno.h>
+   * shadow. <errno.h> is included further down, after ultra64.h. */
   #include <sys/mman.h>
 #endif
 
@@ -52,6 +51,15 @@ extern int snprintf(char *str, size_t maxsize, const char *format, ...);
 #include <ultra64.h>
 #include "bondtypes.h"
 
+#if !defined(PLATFORM_WINDOWS)
+/* Must come after ultra64.h: libc defines `errno` as a macro (glibc:
+ * `(*__errno_location ())`), which would rewrite the N64 `u8 errno;`
+ * fields in PR/os.h (OSContStatus, OSContPad, ...) into a function
+ * declaration and break the build ("field '__errno_location' declared as
+ * a function"). Only the mmap-failure diagnostic below reads errno. */
+  #include <errno.h>
+#endif
+
 #define CART_BASE   0x10000000u
 
 static u8  *rom = NULL;        /* heap copy (fallback path) */