Auto-detect missing hw support for crc32c and fallback to software

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/crc/crc32c.h b/crc/crc32c.h
index 0976261..50f3665 100644
--- a/crc/crc32c.h
+++ b/crc/crc32c.h
@@ -24,8 +24,13 @@
 
 #ifdef ARCH_HAVE_SSE
 extern uint32_t crc32c_intel(unsigned char const *, unsigned long);
+extern int crc32c_intel_works(void);
 #else
 #define crc32c_intel crc32c
+static inline int crc32c_intel_works(void)
+{
+	return 0;
+}
 #endif
 
 #endif