[PATCH v7 1/4] support: Add support_stack_alloc

[Florian Weimer]

* Adhemerval Zanella:

> I have added:
>
>   /* Some architecture still requires executable stack for the signal return                                     
>      trampoline, although PF_X could be overridden if PT_GNU_STACK is present.                                        
>      However since there is glibc does not export such information with a                                        
>      proper ABI, it uses the historical permissions.  */

“since [] glibc does not export”

Thanks,
Florian