swab: protect le32_to_cpu and friends against being defined twice

When used as part of another project, these macros may already be defined.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>

include/swab.h

@@ -41,6 +41,7 @@
                 (__u64)(((__u64)(__x) & (__u64)0xff00000000000000ULL) >> 56) )); \
 })
 
+#ifndef le32_to_cpu
 #if __BYTE_ORDER == __LITTLE_ENDIAN
 
 # define cpu_to_le16(val)                 (val)
@@ -62,5 +63,6 @@
 #else
 # error "nuxi/pdp-endian archs are not supported"
 #endif
+#endif
 
 #endif /* REISERFS_SWAB_H */