cg_llvm: Use LLVM-C bindings for LLVMSetTailCallKind, LLVMGetTypeKind

[Zalathar]

This PR replaces two existing LLVMRust bindings with equivalent calls to the LLVM-C API.

For LLVMGetTypeKind, we avoid the UB hazard by declaring the foreign function to return RawEnum<TypeKind> (which is a wrapper around u32), and then perform checked conversion from u32 to TypeKind.

[rustbot]

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[Zalathar]

cc @WaffleLapkin in case there was some specific reason for the custom LLVMRustSetTailCallKind binding that I didn't think of.