Makefile: Make compiler version comparison optional

Makefile: Make compiler version comparison optional

Forwarded: not-needed
Bug-Debian: https://bugs.debian.org/1019749

The top-level Makefile warns if the compiler version string changes at
all between the kernel build and an out-of-tree module build.

We expect that major compiler version changes could introduce ABI
changes, and override the CC variable in out-of-tree module builds to
ensure that the same major compiler version is used.  But minor
version changes should not make a difference, so this exact version
comparison produces false warnings.

Since custom kernel packages don't have that, don't remove the version
comparison.  Instead, skip it if $(DEBIAN_KERNEL_NO_CC_VERSION_CHECK)
is non-empty.

Gbp-Pq: Topic debian
Gbp-Pq: Name makefile-make-compiler-version-comparison-optional.patch