graphics/png: exclude SIMD from armv{6,7} in QEMU_EMULATING

The current version added an assert for ARM NEON detection, which
is not supported under QEMU_EMULATING, so the build fails. Prevent
exposing the SIMD option in this case.

Approved by: tcberner (mentor)
Differential Revision: https://reviews.freebsd.org/D37212

Author: vishwin

graphics/png/Makefile

@@ -27,6 +27,11 @@ OPTIONS_DEFAULT=APNG
 OPTIONS_DEFAULT_aarch64=	SIMD
 OPTIONS_DEFAULT_amd64=	SIMD
 OPTIONS_DEFAULT_powerpc64le=	SIMD
+# arm/arm_init.c:43:6: error: "No support for run-time ARM Neon checking; use compile-time options"
+.ifdef QEMU_EMULATING
+OPTIONS_EXCLUDE_armv6=	SIMD
+OPTIONS_EXCLUDE_armv7=	SIMD
+.endif
 
 APNG_DESC=Enable Animated PNG support