[llvm] [PowerPC] support tail call optimization on AIX tail call (PR #161690)

[zhijian lin via llvm-commits]

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diggerlin wrote:

for fastcc calling convention in llvm , it is internal use, it do not need to follow the AIX ABI, when the calling convention is fastcc and has tail call optimization option at the same time , it do stack allocate in caller, but the caller  do not do stack free in caller before `b` (jump) to callee, the callee free the stack allocated by caller in callee before return.

https://github.com/llvm/llvm-project/pull/161690