When userland doesn't specify sigaction->sa_restorer, we try to put
the restorer code on the stack. But this breaks ia32 binaries with
non-executable stacks. We now put the restorer code on a gate page.

We still leave the sigreturn code on the stack due to backward 
compatibility concerns with ia32 gdb.

This issue was primarily seen with debian glibc.

	-Arun