Use GetEnvironmentVariable instead of getenv in DebugClient.cc.
Use GetEnvironmentVariable instead of getenv in DebugClient.cc.

This lets libwinpty.dll read the WINPTYDBG environment variable that the
unix adapter sets using SetEnvironmentVariable.  If DebugClient.cc calls
getenv, then it seems to read a copy of the Win32 environment that the
MSVCRT initializes at startup.

traff/winpty,traff/winpty,dscho/winpty,peters/winpty,rprichard/winpty,fracting/winpty,traff/winpty,peters/winpty,peters/winpty,dscho/winpty,rprichard/winpty,fracting/winpty,traff/winpty,rprichard/winpty,dscho/winpty,dscho/winpty,rprichard/winpty,peters/winpty,fracting/winpty,fracting/winpty