Rust cdylib/statliclib support for vendor snapshot.

Adds support for platform vendor_available Rust FFI libraries and
binaries to be included in the vendor snapshot.

Because rlib and dylibs are not yet in snapshots, libstd cannot be
included in a vendor snapshot. As a result, vendor-specific Rust code
can't be guaranteed to work with the platform-provided vendor_available
modules built with a newer toolchain. For now, a check is added
indicating vendor-specific Rust code is unsupported.

This changes the linkage for vendor variants of these modules to default
to rlib linkage since dylibs cannot be included in the snapshot yet.

Bug: 184042776
Test: m nothing # new Soong tests pass
Change-Id: I502eaa4bb962eb87ff868fcf49b435f0d2f982e6

rust/binary.go

@@ -137,6 +137,9 @@ func (binary *binaryDecorator) autoDep(ctx android.BottomUpMutatorContext) autoD
 	// Binaries default to dylib dependencies for device, rlib for host.
 	if binary.preferRlib() {
 		return rlibAutoDep
+	} else if mod, ok := ctx.Module().(*Module); ok && mod.InVendor() {
+		// Vendor Rust binaries should prefer rlibs.
+		return rlibAutoDep
 	} else if ctx.Device() {
 		return dylibAutoDep
 	} else {
@@ -147,6 +150,8 @@ func (binary *binaryDecorator) autoDep(ctx android.BottomUpMutatorContext) autoD
 func (binary *binaryDecorator) stdLinkage(ctx *depsContext) RustLinkage {
 	if binary.preferRlib() {
 		return RlibLinkage
+	} else if ctx.RustModule().InVendor() {
+		return RlibLinkage
 	}
 	return binary.baseCompiler.stdLinkage(ctx)
 }