Subzero: Rename -external to -externalize to match llc.

BUG= none
R=jvoung@chromium.org

Review URL: https://codereview.chromium.org/535623002
diff --git a/src/llvm2ice.cpp b/src/llvm2ice.cpp
index a4a96b9..e704ed3 100644
--- a/src/llvm2ice.cpp
+++ b/src/llvm2ice.cpp
@@ -85,8 +85,8 @@
 TestPrefix("prefix", cl::desc("Prepend a prefix to symbol names for testing"),
            cl::init(""), cl::value_desc("prefix"));
 static cl::opt<bool>
-DisableInternal("external",
-                cl::desc("Disable 'internal' linkage type for testing"));
+DisableInternal("externalize",
+                cl::desc("Externalize all symbols"));
 static cl::opt<bool>
 DisableTranslation("notranslate", cl::desc("Disable Subzero translation"));