Set incremental or codegen-units, not both

This CL changes the handling of Rust flags to only pass one of either
incremental or codegen-units.  This is necessary because incremental
implies a codegen-units value of 128 and it may be overridden by the
separate codegen-units argument.

Test: TH
Change-Id: Ia474e4f9fc071d5054cb479ec9de550fa886677e
diff --git a/rust/config/global.go b/rust/config/global.go
index 4397d58..b94d92f 100644
--- a/rust/config/global.go
+++ b/rust/config/global.go
@@ -44,7 +44,6 @@
 	GlobalRustFlags = []string{
 		"-Z stack-protector=strong",
 		"-Z remap-cwd-prefix=.",
-		"-C codegen-units=1",
 		"-C debuginfo=2",
 		"-C opt-level=3",
 		"-C relocation-model=pic",
@@ -55,7 +54,7 @@
 		// This flag requires to have no space so that when it's exported to bazel
 		// it can be removed. See aosp/2768339
 		"--color=always",
-		"-Zdylib-lto",
+		"-Z dylib-lto",
 		"-Z link-native-libraries=no",
 	}