[Driver] Use shared singleton instance of DriverOptTable

Summary:
This significantly reduces the time required to run clangd tests, by
~10%.

Should also have an effect on other tests that run command-line parsing
multiple times inside a single invocation.

Reviewers: gribozavr, sammccall

Reviewed By: sammccall

Subscribers: kadircet, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D67163

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@370908 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed