I think it makes sense to be able to overwrite the Fortran standard passed to the library (f95, f2003, f2008, gnu, legacy). The reason is that we have several cases where with -std=f95 GNU extensions are rejected. I think not all users are aware of this and combining a compliant Fortran program with libraries which are not can potentially cause problems. And if the source code is not available ...
I therefore think it makes sense to:
a) Note the fact that -std= can change the library behaviour, esp. -std=f95 can reject F2003 or GNU features.
b) Allow the user to overwrite it using an environment variable
Confirmed. I think both the rationale and the proposed actions are clear and sound.