Don't call exit from cl::PrintHelpMessage.

Most callers were not expecting the exit(0) and trying to exit with a
different value.

This also adds back the call to cl::PrintHelpMessage in llvm-ar.

llvm-svn: 312761
diff --git a/llvm/tools/llvm-xray/llvm-xray.cc b/llvm/tools/llvm-xray/llvm-xray.cc
index 98303e7..34c453a 100644
--- a/llvm/tools/llvm-xray/llvm-xray.cc
+++ b/llvm/tools/llvm-xray/llvm-xray.cc
@@ -46,4 +46,5 @@
 
   // If all else fails, we still print the usage message.
   cl::PrintHelpMessage(false, true);
+  return 0;
 }