Fix endianness detection on powerpc (and maybe more BE_ARCHS)

Index: src/physfs_internal.h
--- src/physfs_internal.h.orig
+++ src/physfs_internal.h
@@ -221,6 +221,10 @@ extern void SZIP_global_init(void);
 #include <endian.h>
 #define PHYSFS_BYTEORDER  __BYTE_ORDER
 #else /* __linux__ */
+#ifdef __OpenBSD__
+#include <endian.h>
+#define PHYSFS_BYTEORDER BYTE_ORDER
+#else /* __OpenBSD__ */
 #if defined(__hppa__) || \
     defined(__m68k__) || defined(mc68000) || defined(_M_M68K) || \
     (defined(__MIPS__) && defined(__MISPEB__)) || \
@@ -230,6 +234,7 @@ extern void SZIP_global_init(void);
 #else
 #define PHYSFS_BYTEORDER   PHYSFS_LIL_ENDIAN
 #endif
+#endif /* __OpenBSD__ */
 #endif /* __linux__ */