ffmpeg: enable lto build for arm and x86_64

This toggles on Link-Time Optimization for arm and x86-64.

Compile tested on arm/bcm47xx, arm/mvebu, arm/imx6 and x86-64/generic

(Also compile tested on mips/ar71xx where it failed so this change is currently for specific arches.)

Size savings for libffmpeg were 2-3% when measured with libffmpeg-full and libffmpeg-mini.

Signed-off-by: Ian Leonard <antonlacon@gmail.com>

multimedia/ffmpeg/Makefile

@@ -404,6 +404,8 @@ endif
 
 # selectively disable optimizations according to arch/cpu type
 ifneq ($(findstring arm,$(CONFIG_ARCH)),)
+	FFMPEG_CONFIGURE+= --enable-lto
+
 	ifneq ($(findstring vfp,$(CONFIG_TARGET_OPTIMIZATION)),)
 		FFMPEG_CONFIGURE+= --enable-vfp
 	else
@@ -419,6 +421,10 @@ ifneq ($(findstring arm,$(CONFIG_ARCH)),)
 
 endif
 
+ifeq ($(ARCH),x86_64)
+	FFMPEG_CONFIGURE+= --enable-lto
+endif
+
 ifneq ($(CONFIG_YASM),y)
 FFMPEG_CONFIGURE+= --disable-yasm