CryptoPkg/Library: add -Wno-unused-but-set-variable for openssl

The GCC warning fix is not in 1.1.1x. Ignore the warning type
-Wno-unused-but-set-variable with GCC compiler in the build option.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
Signed-off-by: Gang Chen <gang.c.chen@intel.com>
Reviewed-by: Jiewen Yao <Jiewen.yao@intel.com>