Fix lgtm C++.

Author: benjaminp

CMakeLists.txt

@@ -1,4 +1,5 @@
 cmake_minimum_required(VERSION 3.5)
+include(CheckCXXCompilerFlag)
 project(zstd-jni)
 file(STRINGS "version" NATIVE_VERSION)
 enable_language(C ASM)
@@ -11,4 +12,7 @@ file(GLOB_RECURSE SOURCES RELATIVE ${CMAKE_SOURCE_DIR} "src/*.[cS]")
 add_library(zstd-jni-${NATIVE_VERSION} SHARED ${SOURCES})
 add_definitions("-DZSTD_MULTITHREAD=1")
 add_definitions("-DZSTD_LEGACY_SUPPORT=4")
-add_definitions("-Oz")
+CHECK_CXX_COMPILER_FLAG(-Oz COMPILER_SUPPORTS_OZ)
+if(COMPILER_SUPPORTS_OZ)
+    add_definitions("-Oz")
+endif()