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()
