Add stdlibs property for Rust build rules.

This lets no_std crates depend on system crates like core and alloc.

Bug: 223152204
Test: built pVM firmware skeleton with rust_ffi_static rule
Change-Id: I0f9b0ab3f5e3289fb8ce66f28d779bcf62a7181f
diff --git a/rust/compiler.go b/rust/compiler.go
index c5d40f4..19499fa 100644
--- a/rust/compiler.go
+++ b/rust/compiler.go
@@ -121,6 +121,12 @@
 	// include all of the static libraries symbols in any dylibs or binaries which use this rlib as well.
 	Whole_static_libs []string `android:"arch_variant"`
 
+	// list of Rust system library dependencies.
+	//
+	// This is usually only needed when `no_stdlibs` is true, in which case it can be used to depend on system crates
+	// like `core` and `alloc`.
+	Stdlibs []string `android:"arch_variant"`
+
 	// crate name, required for modules which produce Rust libraries: rust_library, rust_ffi and SourceProvider
 	// modules which create library variants (rust_bindgen). This must be the expected extern crate name used in
 	// source, and is required to conform to an enforced format matching library output files (if the output file is
@@ -360,6 +366,7 @@
 	deps.StaticLibs = append(deps.StaticLibs, compiler.Properties.Static_libs...)
 	deps.WholeStaticLibs = append(deps.WholeStaticLibs, compiler.Properties.Whole_static_libs...)
 	deps.SharedLibs = append(deps.SharedLibs, compiler.Properties.Shared_libs...)
+	deps.Stdlibs = append(deps.Stdlibs, compiler.Properties.Stdlibs...)
 
 	if !Bool(compiler.Properties.No_stdlibs) {
 		for _, stdlib := range config.Stdlibs {
diff --git a/rust/rust.go b/rust/rust.go
index f40f1a8..1c718a4 100644
--- a/rust/rust.go
+++ b/rust/rust.go
@@ -968,6 +968,7 @@
 	deps.ProcMacros = android.LastUniqueStrings(deps.ProcMacros)
 	deps.SharedLibs = android.LastUniqueStrings(deps.SharedLibs)
 	deps.StaticLibs = android.LastUniqueStrings(deps.StaticLibs)
+	deps.Stdlibs = android.LastUniqueStrings(deps.Stdlibs)
 	deps.WholeStaticLibs = android.LastUniqueStrings(deps.WholeStaticLibs)
 	return deps