feat(compiler): Initial support for GOT-based relocations and compact_unwind tables for Mach-O

(Work in progress) macOS uses a different scheme for exception handling
in Mach-O; in contrast with the "usual" .eh_frame mechanism, Mach-O has
a `compact_unwind` section in which EH-related metadata are embedded.
This commit begins the effort to support it in its entirety. On the path
to that end, it also adds GOT-based relocations, which are necessary for
Mach-O object files.

lib/compiler-singlepass/src/compiler.rs

@@ -261,6 +261,7 @@ impl Compiler for SinglepassCompiler {
             function_call_trampolines,
             dynamic_function_trampolines,
             debug: dwarf,
+            got: None,
         })
     }