Disable dsymutil usage on Darwin host

dsymutil is not available during builds. This is disabled by turning off
split-debuginfo.

Bug: 349612831
Bug: 351760165
Test: Pre/post submit
Change-Id: Idd6f00519e303fe02b35ec8c18682afa799f4df4

rust/config/darwin_host.go

@@ -21,7 +21,7 @@ import (
 )
 
 var (
-	DarwinRustFlags     = []string{}
+	DarwinRustFlags     = []string{"-C split-debuginfo=off"}
 	DarwinRustLinkFlags = []string{
 		"-B${cc_config.MacToolPath}",
 	}