build on ARM64 (#21)

Signed-off-by: siddontang siddontang@gmail.com

Copy from https://github.com/facebook/rocksdb/blob/master/CMakeLists.txt#L210

cmake/rocksdb_flags.cmake

@@ -76,6 +76,15 @@ if(CMAKE_SYSTEM_PROCESSOR MATCHES "ppc64le")
   endif(HAS_ALTIVEC)
 endif(CMAKE_SYSTEM_PROCESSOR MATCHES "ppc64le")
 
+if(CMAKE_SYSTEM_PROCESSOR MATCHES "aarch64|AARCH64")
+        CHECK_C_COMPILER_FLAG("-march=armv8-a+crc" HAS_ARMV8_CRC)
+  if(HAS_ARMV8_CRC)
+    message(STATUS " HAS_ARMV8_CRC yes")
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -march=armv8-a+crc -Wno-unused-function")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -march=armv8-a+crc -Wno-unused-function")
+  endif(HAS_ARMV8_CRC)
+endif(CMAKE_SYSTEM_PROCESSOR MATCHES "aarch64|AARCH64")
+
 option(PORTABLE "build a portable binary" OFF)
 option(FORCE_SSE42 "force building with SSE4.2, even when PORTABLE=ON" OFF)
 if(PORTABLE)