Makefile: Enable DELETE_ON_ERROR for all targets

If a target is interrupted in the middle of writing an output file, the
file could be left in a corrupt state. A subsequent make invocation will
see the file as up to date and can cause very confusing errors.

BUG=b:112267918
TEST=Made a target fail before completion and verified make deleted the
output file.

Change-Id: I865827ea769b4dffa638d4324fc7284f6cb2ddc0
Signed-off-by: Raul E Rangel <rrangel@chromium.org>
Reviewed-on: https://review.coreboot.org/27885
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

Makefile

@@ -174,6 +174,7 @@ real-all: real-target
 
 # must come rather early
 .SECONDEXPANSION:
+.DELETE_ON_ERROR:
 
 $(KCONFIG_AUTOHEADER): $(KCONFIG_CONFIG)
 	+$(MAKE) oldconfig