Add rust default compilation flags.

Bug: 140725928
Test: m -j crosvm.experimental
Change-Id: I1674f099659957f024cce70341a6a69610118a69
diff --git a/rust/config/global.go b/rust/config/global.go
index 7846d21..4d87780 100644
--- a/rust/config/global.go
+++ b/rust/config/global.go
@@ -37,6 +37,9 @@
 
 	GlobalRustFlags = []string{
 		"--remap-path-prefix $$(pwd)=",
+		"-C codegen-units=1",
+		"-C opt-level=3",
+		"-C relocation-model=pic",
 	}
 
 	deviceGlobalRustFlags = []string{}