[ExecEnv] Update to work with AmazonLinux1803

[metaskills]

Details: https://aws.amazon.com/blogs/compute/upcoming-updates-to-the-aws-lambda-execution-environment/

[metaskills]

I've decided to use clang and set the --without-magick argument. Each of these progressively got the layer file size down. Details here both zipped and unzipped.

2.8M libvips-master.zip
9.4M libvips-master

2.5M libvips-clang.zip
8.2M libvips-clang

2.4M libvips-clang-without-magick.zip
8.1M libvips-clang-without-magick

Lastly, I cionfirmed that my Lambda using this layer worked prior to this compile change and for all changes here.

[metaskills]

OH! The reason I decided that without imagemagick was OK to commit is that I think it's dynamic usage in Lambda via libvips might have negative side effects. So I felt it was best to do one thing well and get libvips installed with no added gotchas.