[Bug libfortran/80602] Reduce stack usage for blocked matmul

[tkoenig at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80602
Bug 80602 depends on bug 80615, which changed state.

Bug 80615 Summary: [8  Regression] Boostrap fails because genmddeps nees 
not-yet-built libiberty.a
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80615

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID