Move/dedupe some host path functions in package_ctx.go.

These functions don't need a PackageContext object.

Test: m
Bug: 145934348
Change-Id: Ia1da2c76cbad292f9ca79617199b2b5b6b265568

cc/rs.go

@@ -29,7 +29,7 @@ func init() {
 			// Use RenderScript prebuilts for unbundled builds but not PDK builds
 			return filepath.Join("prebuilts/sdk/tools", runtime.GOOS, "bin/llvm-rs-cc")
 		} else {
-			return pctx.HostBinToolPath(ctx, "llvm-rs-cc").String()
+			return ctx.Config().HostToolPath(ctx, "llvm-rs-cc").String()
 		}
 	})
 }