Don't add -lrt on Darwin for sanitized targets.

Bug: 34719251

Change-Id: Iff81c4d891a2341a8152e5603391b55b0222ebd7
diff --git a/cc/sanitize.go b/cc/sanitize.go
index fcb3289..168e6c8 100644
--- a/cc/sanitize.go
+++ b/cc/sanitize.go
@@ -351,7 +351,10 @@
 		if ctx.Host() {
 			flags.CFlags = append(flags.CFlags, "-fno-sanitize-recover=all")
 			flags.LdFlags = append(flags.LdFlags, sanitizeArg)
-			flags.LdFlags = append(flags.LdFlags, "-lrt", "-ldl")
+			if ctx.Os() == android.Linux {
+				flags.LdFlags = append(flags.LdFlags, "-lrt")
+			}
+			flags.LdFlags = append(flags.LdFlags, "-ldl")
 			// Host sanitizers only link symbols in the final executable, so
 			// there will always be undefined symbols in intermediate libraries.
 			_, flags.LdFlags = removeFromList("-Wl,--no-undefined", flags.LdFlags)