meson: add sparse support

Do not use cgcc; instead, extract compilation commands from compile_commands.json
and invoke sparse directly.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/Makefile b/Makefile
index ba8413d..81c9642 100644
--- a/Makefile
+++ b/Makefile
@@ -1261,6 +1261,7 @@
 	$(call print-help,install,Install QEMU, documentation and tools)
 	$(call print-help,ctags/TAGS,Generate tags file for editors)
 	$(call print-help,cscope,Generate cscope index)
+	$(call print-help,sparse,Run sparse on the QEMU source)
 	@echo  ''
 	@$(if $(TARGET_DIRS), \
 		echo 'Architecture specific targets:'; \