Description of problem:
on debian/ubuntu, gcc supports -m 64 flag well enough to
cross-build a 64 bit kernel on a 32 bit OS by using 

Version-Release number of selected component (if applicable):
gcc (GCC) 4.8.2 20131017 (Red Hat 4.8.2-1)


How reproducible:
always

Steps to Reproduce:
1. create a small c file e.g. echo 'void foo(void) {}' > x.c
2. compile with -m 64: gcc -c -m64 -o x.o x.c
3
Actual results:
$ gcc -c -m64 x.c
x.c:1:0: sorry, unimplemented: 64-bit mode not compiled in


Expected results:
create 64 bit object file

Additional info:
this is a requirement for using 64 bit kernels in 32 bit
fedora which I'd like to make work again:
you must be able to build the kernel you are using.