fix r8/r4 configure checks with intel -warn flag

[rem1776]

Description
When compiling with intel the -warn flag breaks the m4 check that looks for real default kind flags. During ./configure when it uses the correct kind default flags with -warn, it gets an error stating There is a conflict between local interface block and external interface block..

This modifies the check to remove the interface block and just use a contains for the subroutine, this way it won't fail on what seems to be a unrelated error.

How Has This Been Tested?
ifort (oneapi 2024.2) with the mkmf debug flags on amd

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included
• make distcheck passes