Install lldb's SB headers (pr36630)
Install lldb's SB headers (pr36630)

These were removed in r309021 in what looks like an accidentally
committed change. This brings them back.

I also rename the header component to lldb-headers (instead of
lldb_headers) to match the llvm style and add a special
install-lldb-headers target, which installs just the headers.

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@327016 91177308-0d34-0410-b5e6-96231b3b80d8

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