Bug 1822216 - Avoid linking C programs with the C++ compiler. r=firefox-build-system-reviewers,ahochheiden

What was added in bug 1378830 was broken by bug 1255485. Not in a super
visible way, but the undesirable side effect is that C programs end up
being linked against the C++ runtime. Which didn't cause practical
problems until bug 1820947.

Differential Revision: https://phabricator.services.mozilla.com/D172519

config/rules.mk

@@ -409,7 +409,7 @@ alltags:
 	find $(topsrcdir) -name dist -prune -o \( -name '*.[hc]' -o -name '*.cp' -o -name '*.cpp' -o -name '*.idl' \) -print | $(TAG_PROGRAM)
 
 define EXPAND_CC_OR_CXX
-$(if $(PROG_IS_C_ONLY_$(1)),$(CC),$(CCC))
+$(if $(PROG_IS_C_ONLY_$(notdir $(1))),$(CC),$(CCC))
 endef
 
 #