Add make rules to generate and upload to coverity

For now, this uses a local installation of coverity's tools in the slink
subfolder.

.gitignore

@@ -74,3 +74,8 @@ fellow_log_dbg
 *.gcda
 *.gcno
 /src/coverage
+
+# coverity
+cov-int
+slash-coverity.xz
+

Makefile.am

@@ -10,3 +10,15 @@ EXTRA_DIST = INSTALL.rst
 
 coverage:
 	$(MAKE) $(AM_MAKEFLAGS) -C src coverage
+
+coverity: clean
+	if [[ -z "$$COVTOKEN" ]] ; then echo need COVTOKEN ; exit 9 ; fi
+	PATH=$$PATH:$$(realpath slink/cov-analysis-*/bin); \
+	cov-build --dir cov-int make -j8 && \
+	tar caf slash-coverity.xz cov-int && \
+	curl --form token="$$COVTOKEN" \
+	--form email=nils.goroll@uplex.de \
+	--form file=@slash-coverity.xz \
+	 --form version=$$(git rev-parse HEAD) \
+	 --form description="Submitted via make coverity" \
+	 https://scan.coverity.com/builds?project=varnish-cache_slash