RPM build scripts for Amazon Linux 2023, x64, Swift 5.8 and 5.9

[sebsto]

This PR adds a new directory under Platforms/Linux/RPM/AmazonLinux to support building RPMs for Amazon Linux 2023.

The main changes are:

• It adds a step to build ld.gold from sources (see [build] fails to build on Amazon Linux 2023 swift#65495) (with this script to download, compile, and install the linker)
• it removes the dependency on Swift Mark GFM that is not required for Swift 5.8+ (see swift-cmark dependency not available for 5.8 RELEASE #261)
• it lets build_script set the required compiler and linker flags, instead of rpmbuild

Additional changes for Swift 5.9

• add dependency on swift-certificates
• add dependency on swift-asn1

Instead of creating one git branch per Swift version, I included Dockerfile and swiftland.spec files for each version. The README file has instructions how to use these files.

This is tested on x64 only

[sebsto]

There is one problem though

Swift 5.8 is a dependency to build Swift 5.9

• When I install Swift 5.8 tar gz file that I built from the Swift project scripts, I can build Swift 5.9.
• When I install Swift 5.8 RPM that I built from the Swift Installer Script scripts, build fails with the following error.

~/swift-project/swift
+ /usr/bin/cmake --build /home/ec2-user/swift-project/build/buildbot_linux/swift-linux-x86_64 -- -j128 all swift-stdlib-linux-x86_64 swift-libexec-linux-x86_64
ninja: error: '/usr/lib/swift/linux/x86_64/swiftrt.o', needed by 'bin/swift-frontend', missing and no known rule to make it

The RPM build is able to compile and run a "Hello Wolrd" app. Basic smoke test is OK.
I have no idea what this error message mean and how to fix this. Any guidance ?

[sebsto]

@shahmishal @futurejones @finagolfin can I get some love for this PR ?
Or tell me how it should be modified ?
Or why it will not be merged ?

I'd like to land this one before sending one for Swift 6.0

Thank you

[finagolfin]

I have never contributed to this repo, so don't know what it is for. Mishal or @tachoknight will have to fill you in.