Convert open options for POSIX open on target platform.

This moves the conversion of the open options to the target platform. On mac fcntl.h has different values for O_CREAT and O_TRUNC than on linux so by transmitting the standardized lldb open options we can correctly convert them on the target platform.

Test Plan:
On linux:
  lldb-server p --listen *:1234
On mac:
  lldb
  platform select remote-linux
  platform connect connect://ip-of-linux-box:1234
  target create ~/path/to/linux/binary
  b main
  process launch
Binary is successfully pushed to linux remote, process successfully launches and break in the main method.

Differential Revision: http://reviews.llvm.org/D8395

llvm-svn: 232634