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

[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 https://github.com/apple/swift/issues/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 https://github.com/apple/swift-installer-scripts/issues/261)
• it lets build_script set the required compiler and linker flags, instead of rpmbuild

This is only tested on x64 and Swift 5.8.

It is known to not work with Swift 5.9. Additional changes are required to build Swift 5.9 (list is not complete) :

• add dependency on swift-certificates
• add dependency on swift-asn1
• (maybe) apply patch https://github.com/apple/swift/pull/69092/files

[sebsto]

@tomerd @shahmishal @compnerd This is a first drop to create the RPM for Swift 5.8, Amazon Linux 2023, x64 I would need this to be published to facilitate the 5.9 build.

What do you think ?