Two changes to scan-build:

Two changes to scan-build:

(1) When no 'clang' is found with 'scan-build', remember the one from
the path as scan-build sees it, not the build system.  This prevents
us from finding different clangs during the build.

(2) Don't set LDPLUSPLUS when running xcodebuild; instead rely on the
clang driver to do the right thing.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@95943 91177308-0d34-0410-b5e6-96231b3b80d8