crossgcc/Makefile.inc: Update jenkins-build-toolchain

Because the builders have the coreboot cross-compilers in their path,
the XGCCPATH variable needs to be set after building the new toolchain
before it will be used.

- Add $DEST/bin to $PATH if $DEST is set, add the default location
for toolchain builds otherwise.  Because the jenkins build image puts
the tools in the path, we ca
- Add KEEP_SOURCES option to help speed up compilation (Slightly).
- Log .xcompile for verification that the right toolchain was used.
- Verify that test-toolchain passes.

Change-Id: I7c270dab94be7e8f801d527169767018a24986e4
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/14231
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

util/crossgcc/Makefile.inc

@@ -69,7 +69,8 @@ endif # ifeq ($(COMPILER_OUT_OF_DATE),1)
 
 # This target controls what the jenkins builder tests
 jenkins-build-toolchain:
-	$(MAKE) crosstools clang \
-		BUILDGCC_OPTIONS='-y --nocolor'
+	$(MAKE) crosstools clang KEEP_SOURCES=1 BUILDGCC_OPTIONS='-y --nocolor'
 	rm -f .xcompile
-	$(MAKE) what-jenkins-does
+	PATH=$(if $(DEST),$(DEST)/bin,$(top)/util/crossgcc/xgcc/bin):$$PATH; $(MAKE) what-jenkins-does
+	-cat .xcompile
+	PATH=$(if $(DEST),$(DEST)/bin,$(top)/util/crossgcc/xgcc/bin):$$PATH; $(MAKE) test-toolchain