s390 depending on cc-options makes it difficult to configure

[Jeremy Cline]

Hi folks,

Commit 5474080a3a0a ("s390/Kconfig: make use of 'depends on cc-option'")
makes it difficult to produce an s390 configuration for Fedora and Red
Hat kernels.

The issue is I have the following configurations:

CONFIG_MARCH_Z13=y
CONFIG_TUNE_Z14=y
# CONFIG_TUNE_DEFAULT is not set

When the configuration is prepared on a non-s390x host without a
compiler with -march=z* it changes CONFIG_TUNE_DEFAULT to y which, as
far as I can tell, leads to a kernel tuned for z13 instead of z14.
Fedora and Red Hat build processes produce complete configurations from
snippets on any available host in the build infrastructure which very
frequently is *not* s390.

I did a quick search and couldn't find any other examples of Kconfigs
depending on march or mtune compiler flags and it seems like it'd
generally problematic for people preparing configurations.

Regards,
Jeremy