package/ffmpeg: force arm mode instead of Thumb mode

Fix the following build failure:
/tmp/ccw5V2Ti.s: Assembler messages:
/tmp/ccw5V2Ti.s:2013: Error: selected processor does not support `itt gt' in Thumb mode
/tmp/ccw5V2Ti.s:2014: Error: Thumb does not support conditional execution
/tmp/ccw5V2Ti.s:2015: Error: Thumb does not support conditional execution
/tmp/ccw5V2Ti.s:2017: Error: selected processor does not support `it le' in Thumb mode
/tmp/ccw5V2Ti.s:2018: Error: Thumb does not support conditional execution
/tmp/ccw5V2Ti.s:2020: Error: selected processor does not support `it gt' in Thumb mode
/tmp/ccw5V2Ti.s:2021: Error: Thumb does not support conditional execution

Fixes:
http://autobuild.buildroot.net/results/3fc/3fc68f756cf1661673941c411c4a2477e901e361/

Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/ffmpeg/ffmpeg.mk

@@ -554,6 +554,10 @@ FFMPEG_CONF_OPTS += --disable-optimizations
 FFMPEG_CFLAGS += -O0
 endif
 
+ifeq ($(BR2_ARM_INSTRUCTIONS_THUMB),y)
+FFMPEG_CFLAGS += -marm
+endif
+
 FFMPEG_CONF_ENV += CFLAGS="$(FFMPEG_CFLAGS)"
 FFMPEG_CONF_OPTS += $(call qstrip,$(BR2_PACKAGE_FFMPEG_EXTRACONF))