Bug 1494038 - Prefix REPORT_BUILD with relativesrcdir; r=firefox-build-system-reviewers,nalexander

This makes it more apparent which directory is responsible for creating
a particular generated file, program, library, etc. It is particularly
helpful in bug 1485081 since all node.py invocations will have similarly
named make targets, but run in different directories.

MozReview-Commit-ID: HlSOiL34i3M

Differential Revision: https://phabricator.services.mozilla.com/D6822

--HG--
extra : moz-landing-system : lando

config/rules.mk

@@ -31,7 +31,7 @@ ifdef REBUILD_CHECK
 REPORT_BUILD = $(info $(shell $(PYTHON) $(MOZILLA_DIR)/config/rebuild_check.py $@ $^))
 REPORT_BUILD_VERBOSE = $(REPORT_BUILD)
 else
-REPORT_BUILD = $(info $(notdir $@))
+REPORT_BUILD = $(info $(relativesrcdir)/$(notdir $@))
 
 ifdef BUILD_VERBOSE_LOG
 REPORT_BUILD_VERBOSE = $(REPORT_BUILD)