Swap -lm and -lpthread for host libc++ users

Match the order we use in make.

Change-Id: I7959f72841bd058b13d6c8fc6efb3c78b5de9d35
diff --git a/cc/cc.go b/cc/cc.go
index eb9c58f..d79cdbe 100644
--- a/cc/cc.go
+++ b/cc/cc.go
@@ -938,7 +938,7 @@
 		if ctx.Host() {
 			flags.CppFlags = append(flags.CppFlags, "-nostdinc++")
 			flags.LdFlags = append(flags.LdFlags, "-nodefaultlibs")
-			flags.LdFlags = append(flags.LdFlags, "-lm", "-lpthread")
+			flags.LdFlags = append(flags.LdFlags, "-lpthread", "-lm")
 			if c.staticBinary() {
 				flags.LdFlags = append(flags.LdFlags, hostStaticGccLibs[ctx.HostType()]...)
 			} else {