Rework how scan-build picks the version of clang to use for static analysis.

Unless the user specifies, the clang used for static analysis is the one
found relative to scan-build.

If the user specifies -with-analyzer, they can pick either to use
the clang bundled with Xcode (via xcrun) or they can specify
a path to clang.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@162620 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed