scan-build: - Only set the environment variable 'CXX' if the user specifies --use-c++. - Fix regression when setting LDPLUSPLUS: add a 'which' to determine the location of g++.  This regression was pointed out by Jordan Breeding!
scan-build:
- Only set the environment variable 'CXX' if the user specifies --use-c++.
- Fix regression when setting LDPLUSPLUS: add a 'which' to determine the location of g++.  This regression was pointed out by Jordan Breeding!


git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@55780 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang