[Developers] MinGW 64 and GDB

[Johnoel Ancheta]

ADMB aims be portable to all compilers.  It is tricky because everyone
has different combinations of compilers and operating systems.  Added
to that is the differences in configuration.  I've tried to improve the build
system to satisfy all users.  Some are happy, some are not so happy.
If we can continue to improve everyday, it should reach a state that all
developers and users are happy with.  In order to reach that state, it is
important to try and test out what is on the HEAD of the ADMB trunk by
as much developers and users.  Having a lot of extra eyes to spot errors
before a release improves the quality of the software.  I apologize for any
issues that was not caught by me or the automated build server.

Johnoel