Mac Catalyst: Read `IPHONEOS_DEPLOYMENT_TARGET` from environment variable to support Clang 13#678

imWildCat wants to merge 2 commits intorust-lang:mainrust-lang/cc-rs:mainfrom

imWildCat:clang-13-mac-catalystimWildCat/cc-rs:clang-13-mac-catalystCopy head branch name to clipboard