7116322: enhance javac make rule with a little bit of instrumentation

Reviewed-by: dholmes, ohair

make/common/Rules.gmk

@@ -233,12 +233,14 @@ classes : $(CLASSES_INIT) .delete.classlist .compile.classlist
 	@$(MKDIR) -p $(CLASSDESTDIR)
 	@$(RM) $<.filtered
 	@$(CAT) $< | $(NAWK) 'length>0' | $(SORT) -u > $<.filtered
-	@if [ `$(CAT) $<.filtered | $(WC) -l` -ge 1 ] ; then \
+	@numfiles=`$(WC) -l < $<.filtered` ; \
+	  if [ $$numfiles -ge 1 ] ; then \
 	    $(ECHO) "# Java sources to be compiled: (listed in file $<)"; \
 	    $(CAT) $<.filtered; \
-	  $(ECHO) "# Running javac:"; \
+	    $(ECHO) "# Running javac: $$numfiles files; in $(CURDIR)"; \
 	    $(ECHO) $(JAVAC_CMD) -sourcepath "$(SOURCEPATH)" -d $(CLASSDESTDIR) @$<.filtered; \
 	    $(JAVAC_CMD) -sourcepath "$(SOURCEPATH)" -d $(CLASSDESTDIR) @$<.filtered; \
+	    $(ECHO) "# javac finished"; \
 	  fi
 	@$(java-vm-cleanup)