PPC/NetBSD: Fix endianess check.

Thanks to he32 and daurnimator.

src/lj_arch.h

@@ -339,7 +339,7 @@
 #if defined(_SOFT_FLOAT) || defined(_SOFT_DOUBLE)
 #error "No support for PowerPC CPUs without double-precision FPU"
 #endif
-#if defined(_LITTLE_ENDIAN)
+#if defined(_LITTLE_ENDIAN) && (!defined(_BYTE_ORDER) || (_BYTE_ORDER == _LITTLE_ENDIAN))
 #error "No support for little-endian PowerPC"
 #endif
 #if defined(_LP64)