Force the pkg-config native tool. Strangely ffmpeg prepends cross_prefix
to the default value which obviously is wrong.

Signed-off-by: Andrei Gherzan <andrei@gherzan.ro>

Index: git/Makefile.ffmpeg
===================================================================
--- git.orig/Makefile.ffmpeg
+++ git/Makefile.ffmpeg
@@ -245,7 +245,8 @@ configure:
 			--disable-decoder=idf \
 			--enable-decoder=opus \
 			--cross-prefix=$(HOST)- \
-			--disable-stripping
+			--disable-stripping \
+			--pkg-config=pkg-config
 
 .PHONY : clean
 clean: