kbuild: Print errors to stderr

... at least in the top-level Makefile and scripts/link-vmlinux.sh.
There are some more instances of the 'echo <error>; exit 1' pattern in
some arch Makefiles and kconfig.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>

scripts/link-vmlinux.sh

@@ -210,8 +210,8 @@ if [ -n "${CONFIG_KALLSYMS}" ]; then
 	mksysmap ${kallsyms_vmlinux} .tmp_System.map
 
 	if ! cmp -s System.map .tmp_System.map; then
-		echo Inconsistent kallsyms data
-		echo echo Try "make KALLSYMS_EXTRA_PASS=1" as a workaround
+		echo >&2 Inconsistent kallsyms data
+		echo >&2 echo Try "make KALLSYMS_EXTRA_PASS=1" as a workaround
 		cleanup
 		exit 1
 	fi