Fix compile failure on Power9

extra/crc32-vpmsum/CMakeLists.txt

@@ -3,6 +3,9 @@ ADD_LIBRARY(crc32c OBJECT vec_crc32.c)
 ADD_LIBRARY(crc32ieee OBJECT vec_crc32.c)
 
 GET_PROPERTY(CFLAGS_CRC32_VPMSUM TARGET ${CRC32_LIBRARY} PROPERTY COMPILE_FLAGS)
+IF (CFLAGS_CRC32_VPMSUM MATCHES "NOTFOUND")
+  SET (CFLAGS_CRC32_VPMSUM "")
+ENDIF()
 SET_TARGET_PROPERTIES(crc32c crc32ieee PROPERTIES  COMPILE_FLAGS "${CFLAGS_CRC32_VPMSUM} -maltivec -mvsx -mpower8-vector -mcrypto -mpower8-vector")
 SET_TARGET_PROPERTIES(crc32ieee PROPERTIES COMPILE_DEFINITIONS "CRC32_FUNCTION=crc32ieee_vpmsum;CRC32_CONSTANTS_HEADER=\"crc32ieee_constants.h\"")
 SET_TARGET_PROPERTIES(crc32c PROPERTIES COMPILE_DEFINITIONS "CRC32_FUNCTION=crc32c_vpmsum;CRC32_CONSTANTS_HEADER=\"crc32c_constants.h\"")