Tweak cmake files to avoid build errors on archs without SIMD support

This is nicer than hardcoding in the port a list of archs with/without
SIMD.  Add an url to this 3.1.x-specific fix, master has more changes
in this area.

Prompted by a diff from matthieu@, ok tb@

graphics/jpeg/Makefile

@@ -26,9 +26,6 @@ MODULES=	devel/cmake
 .if ${MACHINE_ARCH} == "amd64" || ${MACHINE_ARCH} == "i386"
 BUILD_DEPENDS=	devel/nasm
 .endif
-.if ${MACHINE_ARCH} == "sparc64"
-CONFIGURE_ARGS+= -DWITH_SIMD=OFF
-.endif
 
 CONFIGURE_ARGS+= -DCMAKE_INSTALL_PREFIX="${PREFIX}"
 DEBUG_PACKAGES=	${BUILD_PACKAGES}

graphics/jpeg/patches/patch-simd_CMakeLists_txt

@@ -0,0 +1,14 @@
+Don't error out if SIMD isn't available
+https://github.com/libjpeg-turbo/libjpeg-turbo/commit/7cdbf9144d40d68d97c498f54dd88a68aee4e36d
+
+Index: simd/CMakeLists.txt
+--- simd/CMakeLists.txt.orig
++++ simd/CMakeLists.txt
+@@ -3,6 +3,7 @@ macro(simd_fail message)
+     message(FATAL_ERROR "${message}.")
+   else()
+     message(WARNING "${message}.  Performance will suffer.")
++    set(WITH_SIMD 0)
+     set(WITH_SIMD 0 PARENT_SCOPE)
+   endif()
+ endmacro()