Add testcases for riscv machine outliner.

[hiraditya]

Following up from #89822 I guess the first step is to add (potentially failing) test cases that we can work on 1 by 1.

• machine-outliner-leaf-descendants.ll [RISCV] Add testcase for outlining leaf descendants #114450
• machine-outliner-retaddr [RISCV] Add testcase for return address signing for outlined functions #115079
• machine-outliner-tail
• machine-outliner-throw

[llvmbot]

@llvm/issue-subscribers-backend-risc-v

Author: AdityaK (hiraditya)

Following up from #89822 I guess the first step is to add (potentially failing) test cases that we can work on 1 by 1.

• machine-outliner-leaf-descendants.ll
• machine-outliner-retaddr
• machine-outliner-tail
• machine-outliner-throw