Migrate Rust to LLVM coverage.

Bug: 177675913
Test: Manually compile, run, and see output with llvm-cov.
Change-Id: I66729cff87a848782e9fa1b95cbbc06318c5761a
diff --git a/rust/rust_test.go b/rust/rust_test.go
index 48c8d74..fc7f47e 100644
--- a/rust/rust_test.go
+++ b/rust/rust_test.go
@@ -134,7 +134,7 @@
 	if tctx.config == nil {
 		t.Fatalf("tctx.config not been generated yet. Please call generateConfig first.")
 	}
-	tctx.config.TestProductVariables.GcovCoverage = proptools.BoolPtr(true)
+	tctx.config.TestProductVariables.ClangCoverage = proptools.BoolPtr(true)
 	tctx.config.TestProductVariables.Native_coverage = proptools.BoolPtr(true)
 	tctx.config.TestProductVariables.NativeCoveragePaths = []string{"*"}
 }