[PING][PATCH][DJGPP][libgfortran] Do not use S_ISVTX for DJGPP in libfortran/intrinsic/chmod.c

[Andris Pavenis]

Patch avoids using S_ISVTX if it is not defined.

https://gcc.gnu.org/ml/gcc-patches/2015-11/msg01899.html
Initial version of patch avoided it additionally for DJGPP 
(https://gcc.gnu.org/ml/gcc-patches/2015-11/msg01880.html)

Andris