Fix liblua link error when building shared lib under fbcode (#4651)

Summary:
When running `make shared_lib` under fbcode, there's liblua link error: https://gist.github.com/yiwu-arbug/b796bff6b3d46d90c1ed878d983de50d
This is because we link liblua.a when building shared lib. If we want to link with liblua, we need to link with liblua_pic.a instead. Fixing by simply not link with lua.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4651

Differential Revision: D12964798

Pulled By: yiwu-arbug

fbshipit-source-id: 18d6cee94afe20748068822b76e29ef255cdb04d

Makefile

@@ -333,7 +333,7 @@ endif
 ifeq ("$(wildcard $(LUA_LIB))", "") # LUA_LIB does not exist
 $(error $(LUA_LIB) does not exist.  Try to specify both LUA_PATH and LUA_LIB manually)
 endif
-LDFLAGS += $(LUA_LIB)
+EXEC_LDFLAGS += $(LUA_LIB)
 
 endif