ci: improve CI stability with parallel builds, Valgrind, and coverage

Makefile.am

@@ -313,7 +313,7 @@ FUNC_TEST_GROUPS = 1 2 3 4
 
 check-functional-parallel: tests/functionaltests/functionaltests
 	@echo "Running functional tests in parallel ($(words $(FUNC_TEST_GROUPS)) groups)..."
-	@mkdir -p $(builddir)/test-logs
+	@mkdir -p $(builddir)/test-logs $(builddir)/test-files
 	@pids=""; \
 	for g in $(FUNC_TEST_GROUPS); do \
 		./tests/functionaltests/functionaltests $$g > $(builddir)/test-logs/group$$g.log 2>&1 & \
@@ -372,7 +372,10 @@ clean-local:
 	rm -f $(git_include) $(git_include).in
 endif
 
-.PHONY: my-prof.supp
+clean-functional-tests:
+	rm -rf $(builddir)/test-files $(builddir)/test-logs
+
+.PHONY: my-prof.supp clean-functional-tests
 my-prof.supp:
 	@sed '/^# AUTO-GENERATED START/q' prof.supp > $@
 	@printf "\n\n# glib\n" >> $@
@@ -388,7 +391,7 @@ check-unit: tests/unittests/unittests
 	tests/unittests/unittests
 
 @VALGRIND_CHECK_RULES@
-VALGRIND_SUPPRESSIONS_FILES=prof.supp
+VALGRIND_SUPPRESSIONS_FILES=$(srcdir)/prof.supp
 
 # Code coverage targets (requires --enable-coverage)
 coverage-clean: