Clean up exit status and globals procecessing in llvm2ice.

Makes IceTranslator.ExitStatus a boolean (rather than int), and changes
code to check flag when done. Fixes bug introduced in
https://codereview.chromium.org/387023002.

Also cleans up the (Ice) Converter class to handle globals processing,
rathe than doing it in llvm2ice.cpp.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=3894
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/387023002
diff --git a/src/IceTranslator.cpp b/src/IceTranslator.cpp
index 7eb0fc0..4b84688 100644
--- a/src/IceTranslator.cpp
+++ b/src/IceTranslator.cpp
@@ -40,7 +40,7 @@
     }
     if (Func->hasError()) {
       std::cerr << "ICE translation error: " << Func->getError() << "\n";
-      ExitStatus = 1;
+      ErrorStatus = true;
     }
 
     Ice::Timer TEmit;