kbuild: don't enable DEBUG_INFO when building for COMPILE_TEST

It really isn't very interesting to have DEBUG_INFO when doing compile
coverage stuff (you wouldn't want to run the result anyway, that's kind
of the whole point of COMPILE_TEST), and it currently makes the build
take longer and use much more disk space for "all{yes,mod}config".

There's somewhat active discussion about this still, and we might end up
with some new config option for things like this (Andi points out that
the silly X86_DECODER_SELFTEST option also slows down the normal
coverage tests hugely), but I'm starting the ball rolling with this
simple one-liner.

DEBUG_INFO isn't that noticeable if you have tons of memory and a good
IO subsystem, but it hurts you a lot if you don't - for very little
upside for the common use.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/Kconfig.debug

@@ -119,7 +119,7 @@ menu "Compile-time checks and compiler options"
 
 config DEBUG_INFO
 	bool "Compile the kernel with debug info"
-	depends on DEBUG_KERNEL
+	depends on DEBUG_KERNEL && !COMPILE_TEST
 	help
           If you say Y here the resulting kernel image will include
 	  debugging info resulting in a larger kernel image.