Fix the last commit; compression was being enabled on mac native

which led to

ERROR: test_auxv_chunked_reads_work_debugserver (tools/lldb-server/TestGdbRemoteAuxvSupport.py)
ERROR: test_auxv_data_is_correct_size_debugserver (tools/lldb-server/TestGdbRemoteAuxvSupport.py)
ERROR: test_auxv_keys_look_valid_debugserver (tools/lldb-server/TestGdbRemoteAuxvSupport.py)
ERROR: test_qSupported_returns_known_stub_features_debugserver (tools/lldb-server/TestLldbGdbServer.py)

failures because debugserver was advertising compression being available, e.g.

send packet: $qSupported:xmlRegisters=i386,arm,mips#12
read packet: $qXfer:features:read+;PacketSize=20000;qEcho+;SupportedCompressions=zlib-deflate;DefaultCompressionMinSize=384#00

maybe these tests should be a little more accepting of additional
features.  but I didn't mean for this to be enabled on mac native.

llvm-svn: 292890