Adding llvm-shlib to CMake build system with a few new bells and whistles

Summary:
This patch adds a new CMake build setting LLVM_BUILD_LLVM_DYLIB, which defaults to OFF. When set to ON, this will generate a shared library containing most of LLVM. The contents of the shared library can be overriden by specifying LLVM_DYLIB_COMPONENTS. LLVM_DYLIB_COMPONENTS can be set to a semi-colon delimited list of any LLVM components that you llvm-config can resolve.

On Windows, unless you are using Cygwin, you must specify an explicit symbol export file using LLVM_EXPORTED_SYMBOL_FILE. On Cygwin and all unix-like platforms if you do not specify LLVM_EXPORTED_SYMBOL_FILE, an export file containing only the LLVM C API will be auto-generated from the list of LLVM components specified in LLVM_DYLIB_COMPONENTS.

Reviewers: rnk

Reviewed By: rnk

Subscribers: rnk, llvm-commits

Differential Revision: http://reviews.llvm.org/D5890

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220490 91177308-0d34-0410-b5e6-96231b3b80d8
Revert "Don't count inreg params when mangling fastcall functions"

This reverts commit r214981.

I'm not sure what I was thinking when I wrote this. Testing with MSVC
shows that this function is mangled to '@f@8':
  int __fastcall f(int a, int b);

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220492 91177308-0d34-0410-b5e6-96231b3b80d8