* configure.ac: Remove check for libmingw32.

* configure.ac: Remove check for libmingw32.
(SETUP): Define EXE name based on host_cpu.
(MINGWTARGET): Remove.
* Makefile.am: Use SETUP throughout.  Remove MINGWTARGET conditional.
Add -lmingw32 to LDFLAGS.
* ini.h (is_64bit): Declare.
(SETUP_INI_FILENAME): Make dependent on value of is_64bit.
(SETUP_BZ2_FILENAME): Ditto.
* main.cc (is_64bit): Define based on compiler target.
* mount.h (SETUP_KEY_WOW64): Define based on value of is_64bit.
* install.cc (create_allow_protected_renames): Add SETUP_KEY_WOW64
flag to RegOpenKeyEx call.
* mount.cc: Throughout, add SETUP_KEY_WOW64 flag to all RegOpenKeyEx
and RegCreateKeyEx calls.
(read_mounts): Change default Cygwin root depending on is_64bit.