Allow clients to control the exact path that is used to launch processes by...

Allow clients to control the exact path that is used to launch processes by adding new calls to SBLaunchInfo.

The new calls are:

SBFileSpec
SBLaunchInfo::GetExecutableFile ();

void
SBLaunchInfo::SetExecutableFile (SBFileSpec exe_file, bool add_as_first_arg);

<rdar://problem/16833939>

llvm-svn: 208245