kbuild: warn about ld added unique sections

If there is a mixture of specifying sections for code in gcc
and assembler then if the assembler code do not add
the "ax" flags the linker will see this as two different sections
and generate unique sections for each. ld does so by adding a dot
and a number.
Teach modpost to warn if a section shows up that match this
pattern - but do this only for non-debug sections.

It will result in warnings like this:

WARNING: vmlinux.o (.sched.text.1): unexpected section name.
The (.[number]+) following section name are ld generated and not expected.
Did you forget to use "ax"/"aw" in a .S file?
Note that for example <linux/init.h> contains
section definitions for use in .S files.

All warnings seen with a defconfig build for:
x86 (32+64bit) and sparc64 has been fixed (via respective maintainers).

arm, powerpc (64 bit), s390 (32 bit), ia64, alpha, sh4 checked - no
warnings seen with a defconfig build.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>