rust: Add support for CARGO_PKG_NAME

Technically cargo package names and crate names can be different, but
this is rare and usually only a matter of presentation. Adding basic
support in this fashion lets several crates build without adding
significant machinery.

Bug: 276464273
Test: Build a crate which uses this environment variable
Change-Id: I4f4c8c9e277789de7a63be2457f00090e8c3e973
diff --git a/rust/builder.go b/rust/builder.go
index 0dfaef4..bf009a5 100644
--- a/rust/builder.go
+++ b/rust/builder.go
@@ -324,6 +324,7 @@
 			envVars = append(envVars, "CARGO_BIN_NAME="+strings.TrimSuffix(outputFile.Base(), outputFile.Ext()))
 		}
 		envVars = append(envVars, "CARGO_CRATE_NAME="+ctx.RustModule().CrateName())
+		envVars = append(envVars, "CARGO_PKG_NAME="+ctx.RustModule().CrateName())
 		pkgVersion := ctx.RustModule().compiler.CargoPkgVersion()
 		if pkgVersion != "" {
 			envVars = append(envVars, "CARGO_PKG_VERSION="+pkgVersion)