Re: after r114507 cannot build on msys - dup2 problem

[Jarek Czekalski <jarekczek@poczta.onet.pl>]

If there are ever any problems with dup2 here is my analyze:

Emacs code never uses the feature of dup2, that it returns the 
descriptor. In most cases the return value is ignored. In emacs.c the 
return value is tested for < 0, which is compatible with both msvcrt and 
posix.

So the test in m4/dup2.m4 whether dup2(1, 1) returns 1 is not needed and 
could be skipped.

Other tests for dup2 are passed on mingw.

Jarek