[profile] use GetComputerNameExW instead of gethostname on Windows

Summary: In profile data paths, we replace "%h" with the hostname of the machine the program is running on. On Windows, we used gethostname() to obtain the hostname. This requires linking with ws2_32. With this change, we instead get the hostname from GetComputerNameExW(), which does not require ws2_32.

Reviewers: rnk, vsk, amccarth

Subscribers: zturner, ruiu, hans

Differential Revision: https://reviews.llvm.org/D27178

llvm-svn: 288146