Define InitLLVM to do common initialization all at once.

We have a few functions that virtually all command wants to run on
process startup/shutdown. This patch adds InitLLVM class to do that
all at once, so that we don't need to copy-n-paste boilerplate code
to each llvm command's main() function.

Differential Revision: https://reviews.llvm.org/D45602

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@330046 91177308-0d34-0410-b5e6-96231b3b80d8
40 files changed