Fix building tests without system headers on Darwin
Fix building tests without system headers on Darwin

Summary: Default installations of OS X do not have system headers installed at /usr/include. This patch allows the LLDB test executables to properly compile when built on a system without headers at /usr/include by specifying a default value for the apple-sdk flag as "macosx".

Reviewers: tfiala, zturner

Subscribers: lldb-commits

Differential Revision: https://reviews.llvm.org/D25487

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@284042 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb