libgfortran trunk build failure, x86_64-pc-cygwin, MINGW64_VERSION_MAJOR defined

[Tim Prince]

libtool: compile: 
/cygdrive/c/users/tim/tim/tim/src/gnu/gcc2/cyg64/./gcc/gfortr
an -B/cygdrive/c/users/tim/tim/tim/src/gnu/gcc2/cyg64/./gcc/
-B/usr/local/gcc7/x
86_64-unknown-cygwin/bin/ -B/usr/local/gcc7/x86_64-unknown-cygwin/lib/
-isystem
/usr/local/gcc7/x86_64-unknown-cygwin/include -isystem
/usr/local/gcc7/x86_64-un
known-cygwin/sys-include -I . -Wall -Werror -fimplicit-none
-fno-repack-arrays -
fno-underscoring -fallow-leading-underscore -g -O2 -c
../../../libgfortran/intri
nsics/selected_real_kind.f90 -o selected_real_kind.o >/dev/null 2>&1

../../../libgfortran/intrinsics/random.c: In function ‘getosrandom’:
../../../libgfortran/intrinsics/random.c:310:5: error: implicit
declaration of function ‘rand_s’; did you mean ‘rand_r’?
[-Werror=implicit-function-declaration]

     rand_s (&b[i]);
     ^~~~~~
     rand_r

cc1: some warnings being treated as errors

I'm hoping you can suggest how you would like this done. 
--disable-werror is set but you appear to be over-riding it again, under
that non-sensical #ifdef __MINGW64_VERSION_MAJOR which I will ifdef out
again.