Patch for MSVC compilation

[Michael Goffioul]

Hi,

I'd like to commit the following patch. Any objection?
It does the following:
- adapt configure script to use MSVC with *mingw*
  build host + some fixes related to the move to gnulib
  (search for -ldirent, add -ladvapi32...)
- fix the problem reported in [1]
- add "round" to the gnulib modules [2]

[1] 
http://old.nabble.com/Problem-with-sys-time.h,-not-using-gnulib-provided-one-to27170247.html#a27170247

[2] round is actually used by the "times" module, not directly
by octave; maybe the correct solution would be to make the
times module dependent on round; anyway, iirc the mingw
implementation of round was buggy, so it might be good to use
that module directly in octave and simplify the code of xround

Michael.

msvc_compile_safe
Description: Binary data