cppcheck: Don't check the system headers

We pass -I options to cppcheck so that it will find the system headers.
Then we need to pass a bunch more options to suppress the zillions of
cppcheck errors found in those headers.

It turns out, however, that it's not recommended to give the system headers
to cppcheck anyway.  Instead it has built-in knowledge of the ANSI libc and
uses that as the basis of its checks.  We do need to suppress
missingIncludeSystem warnings instead though.

Not bothering with the system headers makes the cppcheck runtime go from
~37s to ~14s on my machine, which is a pretty nice win.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Makefile

@@ -163,11 +163,6 @@ clang-tidy: $(PASST_SRCS) $(HEADERS)
 	clang-tidy $(PASST_SRCS) -- $(filter-out -pie,$(FLAGS) $(CFLAGS) $(CPPFLAGS)) \
 	           -DCLANG_TIDY_58992
 
-SYSTEM_INCLUDES := /usr/include $(wildcard /usr/include/$(TARGET))
-ifeq ($(shell $(CC) -v 2>&1 | grep -c "gcc version"),1)
-VER := $(shell $(CC) -dumpversion)
-SYSTEM_INCLUDES += /usr/lib/gcc/$(TARGET)/$(VER)/include
-endif
 cppcheck: $(PASST_SRCS) $(HEADERS)
 	if cppcheck --check-level=exhaustive /dev/null > /dev/null 2>&1; then \
 		CPPCHECK_EXHAUSTIVE="--check-level=exhaustive";		\
@@ -177,11 +172,8 @@ cppcheck: $(PASST_SRCS) $(HEADERS)
 	cppcheck --std=c11 --error-exitcode=1 --enable=all --force	\
 	--inconclusive --library=posix --quiet				\
 	$${CPPCHECK_EXHAUSTIVE}						\
-	$(SYSTEM_INCLUDES:%=-I%)					\
-	$(SYSTEM_INCLUDES:%=--config-exclude=%)				\
-	$(SYSTEM_INCLUDES:%=--suppress=*:%/*)				\
-	$(SYSTEM_INCLUDES:%=--suppress=unmatchedSuppression:%/*)	\
 	--inline-suppr							\
+	--suppress=missingIncludeSystem \
 	--suppress=unusedStructMember					\
 	$(filter -D%,$(FLAGS) $(CFLAGS) $(CPPFLAGS)) -D CPPCHECK_6936  \
 	$(PASST_SRCS) $(HEADERS)