[llvm-c] Improve TargetMachine bindings

[dtcxzyw]

This PR exposes four APIs for TargetMachine:

/** Enable fast-path instruction selection. */
void LLVMSetTargetMachineFastISel(LLVMTargetMachineRef T, LLVMBool Enable);

/** Enable global instruction selection. */
void LLVMSetTargetMachineGlobalISel(LLVMTargetMachineRef T, LLVMBool Enable);

/** Set abort behaviour when global instruction selection fails to lower/select
 * an instruction. */
void LLVMSetTargetMachineGlobalISelAbort(LLVMTargetMachineRef T,
                                         LLVMGlobalISelAbortMode Mode);

/** Enable the MachineOutliner pass. */
void LLVMSetTargetMachineMachineOutliner(LLVMTargetMachineRef T,
                                         LLVMBool Enable);

Fixes #70666.

[dexonsmith]

(Removed myself from the review list, since I wouldn't say I'm up enough on either TargetMachine or the C API.)

[wjakob]

Perfect! I have never used the machine outliner and can't comment on how useful that is. But having controllability over FastISel/SelectionDag/GlobalISel is 💯

[dtcxzyw]

It seems like this commit breaks some build bots. I will fix it later.

[dtcxzyw]

Oh, it has been addressed by ad1b7a4. @joker-eph Thank you for your fix!