Extract library-specific elements to separate files

[KostasTsiounis]

For each of the platform-specific makefiles, the rules and variables that are applicable to all potential native libraries are extracted to common makefiles.

The original makefiles only maintain the library-specific elements and include the equivalent common makefiles for the rest of them.

Back-ported from: #1419

Signed-off-by: Kostas Tsiounis kostas.tsiounis@ibm.com

[KostasTsiounis]

The difference in lines between this and the 25+ versions is due to the following reasons:

• AIX has been updated to use the ibm-clang_r compiler in later versions, which requires different flags => I've maintained the appropriate compiler per version
• z/OS has also been updated to use the ibm-clang64 compiler in later versions, which requires different flags => I've synced all versions given that they probably won't be directly used
• There was a discrepancy in the displaycompiler rule in the linux makefile => it has been synced up to main in all versions