[Bug bootstrap/77359] [7 Regression] AIX bootstrap failure due to alignment of stack pointer + STACK_DYNAMIC_OFFSET

["vogt at linux dot vnet.ibm.com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77359

--- Comment #13 from Dominik Vogt <vogt at linux dot vnet.ibm.com> ---
> What do you mean by size of a stack slot?

On s390, if we have one "int" variables on the stack, this uses a "slot" 4
bytes.  The stack pointer maintains an 8 byte alignmet though, i.e. SP is
changec by 8.  If we have two "int" on the stack, they use a 4 byte slot each,
and the SP is still changed by just 8.  The 4 bytes is what the s390 Abi calls
a stack "slot" which is the minimum allocation unit for variables on the stack,
i.e. whatever a variable needs is rouded up to a multiple of 4.  When this is
done, the final sum of needed stack space (including the dynamic stack area) is
rounded up to STACK_BOUNDARY.  Actually I don't know if any other target has
something similar.