Darwin/Mac OS host rust compilation fixes

- Don't pass `--as-needed` to the linker on Mac OS which is unsupported
  there
- Use `--force_load` rather than `--Wl,--whole-archive` on Mac OS
- Scan `rustc`'s linker arguments for `-dylib` and `-dynamiclib`, which
  it can use instead of `-shared` on Mac OS:
  7bd81ee190/compiler/rustc_codegen_ssa/src/back/linker.rs (L319)

Test: m libhalf serde_derive
Bug: 291164566
Change-Id: Iecd6c2532fa31c9476834f49b109de98cbd2dccf

rust/config/global.go

@@ -102,7 +102,6 @@ func init() {
 
 	pctx.ImportAs("cc_config", "android/soong/cc/config")
 	pctx.StaticVariable("RustLinker", "${cc_config.ClangBin}/clang++")
-	pctx.StaticVariable("RustLinkerArgs", "-Wl,--as-needed")
 
 	pctx.StaticVariable("DeviceGlobalLinkFlags", strings.Join(deviceGlobalLinkFlags, " "))