Three little cleanups in the debugserver xcode project file.

1. Link against libpmenergy and pmsample unconditionally.  It is available on 
macOS 10.10 ("Yosemite") and newer.  We're already linking against libcompression
unconditionally which is only available on macOS 10.11 & newer.

2. Change a few "sdk=macosx.internal"'s to sdk=macosx.

3. Clean up a few places where libcompression was being enabled inconsistently.


Note: the -DLLDB_ENERGY define is only set when building against the macosx.internal
SDK; it includes a header file that is not public.  We link against the dylibs
unconditionally for simplicity.

llvm-svn: 327084