Makefile: add cleanup of pkg-config files created by configure to distclean

Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>

Makefile

@@ -181,6 +181,7 @@ clean::
 distclean::
 	$(RM) $(DISTCLEANSUFFIXES)
 	$(RM) config.* .config libavutil/avconfig.h .version avversion.h version.h libavutil/ffversion.h libavcodec/codec_names.h
+	$(RM) -rf doc/examples/pc-uninstalled
 
 config:
 	$(SRC_PATH)/configure $(value FFMPEG_CONFIGURATION)