Fix a corruption issue when LLVM is used as a shared library in a plugin
Consider the case where A depends on B depends on LLVM, where B is a
shared compiler library built on LLVM that defines command-line options
(cl::opt) because it can also be used in a non-plugin setting.
If A is loaded and unloaded multiple times, causing B to be loaded and
unloaded multiple times while LLVM *isn't* unloaded, then corruption
results without this change: as B is unloaded, its cl::opt globals
disappear but the GlobalParser still holds a (dangling) reference to
them. Furthermore, if A and B are loaded a second time, the cl::opt
globals are constructed again which fails because options of the same
name are still registered.
The straightforward fix is to remove cl::opts from the GlobalParser in