MI fix allowing multiple logging instances of lldb-mi to run simultaneously.

Summary:
Currently if two instances of lldb-mi are running with logging enabled using '--log' the log file conflicts. This produces the following error 
MI: Error: File Handler. Error Permission denied opening 'C:\Users\Ewan\LLVM\build\Debug\bin\lldb-mi-log.txt'

Fixed in this patch by renaming lldb-mi-log.txt based on the date, e.g. lldb-mi-log.txt-20150316163631.log, and moving the file into the temp directory by using the --log-dir option.

Regrading previous review comments the P_tmpdir macro is defined in Windows but always points to "\", which doesn't help much. Also when using the Windows API for GetTempPath() dynamic memory seems much more messy.

Patch from ewan@codeplay.com

Reviewers: abidh, EwanCrawford

Subscribers: zturner, lldb-commits, deepak2427

Differential Revision: http://reviews.llvm.org/D9054

llvm-svn: 235589