kconfig: show compiler version text in the top comment

This is a side-port of commit 21c54b774744 ("kconfig: show compiler
version text in the top comment") from Linux:

"The kernel configuration phase is now tightly coupled with the compiler
in use.  It will be nice to show the compiler information in Kconfig."

We have already had the required makefile logic for this and had not
included printing the value in various user and file visible places.

Cc: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Tom Rini <trini@konsulko.com>