More warnings with libgfortran

[NightStrike]

../../../gcc/libgfortran/io/write.c: In function 'write_a_char4':
../../../gcc/libgfortran/io/write.c:335: warning: passing argument 2
of 'write_default_char4' from incompatible pointer type
../../../gcc/libgfortran/io/write.c:51: note: expected 'gfc_char4_t *'
but argument is of type 'const char *'


I get the above when compiling for x86_64-pc-mingw32.  I'd supply a
patch to silence them, but unfortunately, I don't know how.