updates wrt 32 / 64 bit guests

Some -m32 / -m64 have been left behind.  Here are patches to remove them.

Note that some of the -m32 in qemu/configure look very suspicious to me.  I'm not sure if they are locally patched or not though.  But all remaining occurrences of -m32 / -m64 should likely be checked.

Also change all build instructions that talk of 32-bit only guests.  S2E supports 64-bit guests nowadays.