contrib: ffmpeg: also pass ranlib to configure

This is particularily needed when ar and $(HOST)-ar are not producing
the same type of archive, like linux -> iOS cross compilation.

(cherry picked from commit b0583e76fd3fec8d0b57b1b2581ab28b9c35ae17)

Signed-off-by: Steve Lhomme <robux4@ycbcr.xyz>

contrib/src/ffmpeg/rules.mak

@@ -213,7 +213,7 @@ ifeq ($(call need_pkg,"libavcodec >= $(FFMPEG_LAVC_MIN) libavformat >= 53.21.0 l
 PKGS_FOUND += ffmpeg
 endif
 
-FFMPEGCONF += --nm="$(NM)" --ar="$(AR)"
+FFMPEGCONF += --nm="$(NM)" --ar="$(AR)" --ranlib="$(RANLIB)"
 
 $(TARBALLS)/ffmpeg-$(FFMPEG_BASENAME).tar.xz:
 	$(call download_git,$(FFMPEG_GITURL),,$(FFMPEG_HASH))