Fix typos in arch_list and do variant validation

Test: m nothing
Change-Id: Icfbc9f886a1e16abe02bf6c61671b8187a699942
diff --git a/cc/config/x86_64_device.go b/cc/config/x86_64_device.go
index d789cde..0da51cb 100644
--- a/cc/config/x86_64_device.go
+++ b/cc/config/x86_64_device.go
@@ -37,10 +37,10 @@
 		"": []string{
 			"-march=x86-64",
 		},
+
 		"broadwell": []string{
 			"-march=broadwell",
 		},
-
 		"haswell": []string{
 			"-march=core-avx2",
 		},