RFR: Add support for AIX in build process

[Suchismith Roy]

Summary of the issues: 

1. There is no support for compiling AIX dynamic .a library and the tool was compiling .so files instead. 
2. There is no logic to support libclang.a. 
3.  There is no support to load shared member of .a dynamic libraries of AIX. 

JBS Issue: [CODETOOLS-7904116](https://bugs.openjdk.org/browse/CODETOOLS-7904116)

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Commit messages:
 - remove executable
 - remove extra changes
 - library loading logic
 - build file changes
 - gradle fixes
 - jextract: Cleanup of Index_h
 - cmake support
 - jextract: Enable loading of dynamic archives for AIX

Changes: https://git.openjdk.org/jextract/pull/297/files
  Webrev: https://webrevs.openjdk.org/?repo=jextract&pr=297&range=00
  Stats: 416 lines in 7 files changed: 113 ins; 273 del; 30 mod
  Patch: https://git.openjdk.org/jextract/pull/297.diff
  Fetch: git fetch https://git.openjdk.org/jextract.git pull/297/head:pull/297

PR: https://git.openjdk.org/jextract/pull/297