Use fcntl.h to retrieve the O_CREAT and O_RDWR constants.

Summary:
Normally, these macros are defined in fnctl.h. However, GLIBC exposes their
definition through <sys/file.h> too. This change allows us to compile
LLDB with non-GLIBC C libraries.

Reviewers: clayborg

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D13022

llvm-svn: 248255