build: Ignore generated mapfile and remove it on distclean

.gitignore

@@ -26,3 +26,4 @@
 /config.*
 /coverage.info
 /lcov/
+/mapfile

Makefile

@@ -218,7 +218,7 @@ clean::
 distclean::
 	$(RM) $(DISTCLEANSUFFIXES)
 	$(RM) config.* .config libavutil/avconfig.h .version avversion.h \
-          libavcodec/bsf_list.c libavformat/protocol_list.c
+            mapfile libavcodec/bsf_list.c libavformat/protocol_list.c
 
 config:
 	$(SRC_PATH)/configure $(value LIBAV_CONFIGURATION)