Replace Rust global arg with more legible alternative

Bug: 201431719
Test: m rust
Change-Id: I5e0fae74e1df02f059ddcfa004b29059126a52e0
diff --git a/rust/config/global.go b/rust/config/global.go
index 23384e5..2821e31 100644
--- a/rust/config/global.go
+++ b/rust/config/global.go
@@ -41,7 +41,7 @@
 	}
 
 	GlobalRustFlags = []string{
-		"--remap-path-prefix $$(pwd)=",
+		"-Z remap-cwd-prefix=.",
 		"-C codegen-units=1",
 		"-C debuginfo=2",
 		"-C opt-level=3",