Implement a simple cache in headersearch.  This speeds up
preprocessing 483.xalancbmk by about 10%, reducing the number
of file lookup queries from 2139411 to 199466 (over 10x)


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@40390 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed