* Harmonize the subsystem of every binary to CONSOLE. It apparently
doesn't matter for DLLs, and it's easier if they're all the same. I
examined various DLLs on my system, and they're very inconsistent.
(e.g. kernel32.dll is CONSOLE, but shell32.dll is GUI.)
* When using a recent XP-targeting toolset (v120_xp or v140_xp), it's
necessary to explicitly specify the subsystem, so list it in
configurations.gypi.
* node.js changed its common.gypi to disable exception handling[1], so
explicitly turn it back on in winpty.gyp. Placing the setting in
winpty.gyp's 'target_defaults' block doesn't seem to override a setting
in an included file's 'target_defaults' block, so instead enable EH on
each target.
* For consistency with other gyp files I see, use quoted integers instead
of bare integers for settings. Affects the 'RuntimeLibrary' setting.
* Provide a documented way in configurations.gypi for setting the
XP-specific toolsets.
[1] da9eff80a3
3733682d2f