Add missing PVS Studio Open Source comments.

Also avoid checking protobuf-c source and protobuf-c generated files.

lib/protobuf-c/Makefile.in

@@ -81,11 +81,6 @@ POBJS = $(IOBJS:.i=.plog)
 
 all: libprotobuf-c.la
 
-pvs-log-files: $(POBJS)
-
-pvs-studio: $(POBJS)
-	plog-converter $(PVS_LOG_OPTS) $(POBJS)
-
 depend:
 	$(scriptdir)/mkdep.pl --srcdir=$(abs_top_srcdir) \
 	    --builddir=$(abs_top_builddir) lib/protobuf-c/Makefile.in
@@ -144,7 +139,9 @@ splint:
 cppcheck:
 	cppcheck $(CPPCHECK_OPTS) -I$(incdir) -I$(top_builddir) -I$(top_srcdir) $(srcdir)/*.c
 
-pvs-log-files: $(POBJS)
+pvs-log-files:
+
+pvs-studio:
 
 fuzz: