[lldb/CMake] Initialize LLDB_ENABLE_POSIX based on the UNIX variable.

Author: JDevlieghere

lldb/cmake/modules/LLDBGenerateConfig.cmake

@@ -24,7 +24,11 @@ check_library_exists(compression compression_encode_buffer "" HAVE_LIBCOMPRESSIO
 # so that the check isn't duplicated, but we translate them into the LLDB names
 # so that I don't have to change all the uses at the moment.
 set(LLDB_ENABLE_TERMIOS ${HAVE_TERMIOS_H})
-set(LLDB_ENABLE_POSIX NOT UNIX)
+if (UNIX)
+  set(LLDB_ENABLE_POSIX ON)
+else()
+  set(LLDB_ENABLE_POSIX OFF)
+endif()
 
 if(NOT LLDB_CONFIG_HEADER_INPUT)
  set(LLDB_CONFIG_HEADER_INPUT ${LLDB_INCLUDE_ROOT}/lldb/Host/Config.h.cmake)