[BOLT][AArch64] Implement PLTCall optimization

`convertCallToIndirectCall` applies the PLTCall optimization and returns
an (updated if needed) iterator to the converted call instruction.
Since AArch64 requires to inject additional instructions to implement this
pass, the relevant BasicBlock and an iterator was passed to the
`convertCallToIndirectCall`.

`NumCallsOptimized` is updated only on successful application of the pass.

Tests:
- Inputs/plt-tailcall.c: an example of a tail call optimized PLT call.
- AArch64/plt-call.test: it is the actual A64 test, that runs the PLTCall
  optimization on the above input file and verifies the application of
  the pass to the calls: 'printf' and 'puts'.