contrib: ffmpeg: enable thumb

Depends on --enable-small and HAVE_NEON
If we use NEON, we assume at least cortex-a8 CPU which means thumb2 is supported

contrib/src/ffmpeg/rules.mak

@@ -33,6 +33,12 @@ endif
 
 ifdef ENABLE_SMALL
 FFMPEGCONF += --enable-small --optflags=-O2
+ifeq ($(ARCH),arm)
+ifdef HAVE_NEON
+# XXX: assumes CPU >= cortex-a8, and thus thumb2 able
+FFMPEGCONF += --enable-thumb
+endif
+endif
 endif
 
 # XXX: REVISIT