Makefile: Set retpoline cflags based on CONFIG_CC_IS_{CLANG,GCC}

stable inclusion
from stable-v5.10.133
commit 37b9bb094123a14a986137d693b5aa18a240128b
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5PTAS
CVE: CVE-2022-29900,CVE-2022-23816,CVE-2022-29901

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=37b9bb094123a14a986137d693b5aa18a240128b



--------------------------------

This was done as part of commit 7d73c3e9
"Makefile: remove stale cc-option checks" upstream, and is needed to
support backporting further retpoline changes.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Lin Yujun <linyujun809@huawei.com>
Reviewed-by: Zhang Jianhua <chris.zjh@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>