CHROMIUM: make "command not found" QA warnings fatal

Upstream doesn't have a way of making these fatal, only QA warnings.
Make them fatal for all our builds to avoid things slipping through.

BUG=chromium:821145
TEST=CQ passes

Change-Id: I480854b23accfdcee046cb70893e4cff1f2a8b04
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/portage_tool/+/1772039
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/lib/_emerge/EbuildPhase.py b/lib/_emerge/EbuildPhase.py
index 4104cef..bb2088b 100644
--- a/lib/_emerge/EbuildPhase.py
+++ b/lib/_emerge/EbuildPhase.py
@@ -241,7 +241,9 @@
 
 		if self.phase == "install":
 			out = io.StringIO()
-			_check_build_log(self.settings, out=out)
+			ret = _check_build_log(self.settings, out=out)
+			if ret is False:
+				fail = True
 			msg = out.getvalue()
 			self.scheduler.output(msg, log_path=logfile)
 
diff --git a/lib/portage/package/ebuild/doebuild.py b/lib/portage/package/ebuild/doebuild.py
index 87c793a..65b6e39 100644
--- a/lib/portage/package/ebuild/doebuild.py
+++ b/lib/portage/package/ebuild/doebuild.py
@@ -1943,6 +1943,8 @@
 	if f_real is not None:
 		f_real.close()
 
+	return not bash_command_not_found
+
 def _post_src_install_write_metadata(settings):
 	"""
 	It's possible that the ebuild has changed the