rust: strip libraries and binaries

Reuses the cc.Stripper logic. Abstracts Stripper to avoid the spreading
of references to the cc package.

rustc requires unstripped libraries (precisely, with the `.rustc`
section) when building dependent targets. Contrary to cc, the output of
a compiler module will remain unstripped and only an extra build rule
will be added. This rule will be referenced at install time (in
baseCompiler.install or androidmk).

This change drastically reduces the size of the installed libraries:
(unstripped, from out/target/product/crosshatch/system)
$ find . -name \*.dylib.so -print0 | du -c --files0-from=-
149996  total

(stripped, with this change)
$ find . -name \*.dylib.so -print0 | du -c --files0-from=-
42380   total

Bug: 153430439
Test: cd external/rust; mma
Change-Id: I94fd8bbcec97e0610aa325d3db4460be84d01734

rust/strip.go

@@ -0,0 +1,30 @@
+// Copyright 2020 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package rust
+
+import (
+	"android/soong/android"
+	"android/soong/cc"
+)
+
+// Stripper encapsulates cc.Stripper.
+type Stripper struct {
+	cc.Stripper
+}
+
+func (s *Stripper) StripExecutableOrSharedLib(ctx ModuleContext, in android.Path, out android.ModuleOutPath) {
+	ccFlags := cc.StripFlags{Toolchain: ctx.RustModule().ccToolchain(ctx)}
+	s.Stripper.StripExecutableOrSharedLib(ctx, in, out, ccFlags)
+}