Stablish rule for submodule procedures declaration compatible with older cmake versions

[jalvesz]

Motivation

I have had problems with this issue https://gitlab.kitware.com/cmake/cmake/-/issues/18427#note_983426 when compiling stdlib under systems with cmake 3.17.5 (which for several reasons can't be upgraded) and then having build errors with spurious modules.

I had to patch locally the procedures by replacing for instance module pure function by pure module function etc etc.

I would like to propose that module procedures are to be declared as:
<attribute> <attribute> module <function/subroutine> <name>
instead of
module <attribute> <attribute> <function/subroutine> <name>

This would ensure an easy retro compatibility.

Affected modules :
stdlib_system_subprocess
stdlib_system
stdlib_linalg_diag
stdlib_linalg

Prior Art

No response

Additional Information

No response