mjpegtools: fix build on powerpc without altivec

mpjegtools fails to build on powerpc without altivec:

build_sub44_mests.c: In function 'build_sub44_mests_altivec':
build_sub44_mests.c:268:9: internal compiler error: Segmentation fault
     vr1 = vec_ld(rowstride, (unsigned char*)s44blk);

It seems mpjegtools is wrongly detecting altivec support:
configure:   - PowerPC Optimizations:
configure:     - AltiVec enabled             : true

Fix this by adding BR2_PACKAGE_MJPEGTOOLS_SIMD_SUPPORT and setting
--enable-simd-accel / --disable-simd-accel

Fixes:
 - http://autobuild.buildroot.net/results/c9464712f43efb8954fd2e5460126ad193660353

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/mjpegtools/Config.in

@@ -12,6 +12,11 @@ config BR2_PACKAGE_MJPEGTOOLS
 
 	  http://mjpeg.sourceforge.net
 
+config BR2_PACKAGE_MJPEGTOOLS_SIMD_SUPPORT
+	bool
+	default y if BR2_X86_CPU_HAS_MMX
+	default y if BR2_POWERPC_CPU_HAS_ALTIVEC
+
 comment "mjpegtools needs a toolchain w/ C++, threads"
 	depends on BR2_USE_MMU
 	depends on !BR2_INSTALL_LIBSTDCPP || !BR2_TOOLCHAIN_HAS_THREADS

package/mjpegtools/mjpegtools.mk

@@ -10,6 +10,12 @@ MJPEGTOOLS_DEPENDENCIES = host-pkgconf jpeg
 MJPEGTOOLS_LICENSE = GPL-2.0+
 MJPEGTOOLS_LICENSE_FILES = COPYING
 
+ifeq ($(BR2_PACKAGE_MJPEGTOOLS_SIMD_SUPPORT),y)
+MJPEGTOOLS_CONF_OPTS += --enable-simd-accel
+else
+MJPEGTOOLS_CONF_OPTS += --disable-simd-accel
+endif
+
 ifeq ($(BR2_PACKAGE_LIBPNG),y)
 MJPEGTOOLS_CONF_OPTS += --with-libpng
 MJPEGTOOLS_DEPENDENCIES += libpng