Fortran: Subsume F90 check into ABI check

Follow the approach from commit 1d21dd0f7c (enable_language: Assume
compiler works if ABI detection compiles, 2020-05-25, v3.18.0-rc1~93^2)
to avoid a redundant check for F90 support.  Almost all maintained
Fortran compilers support F90 these days.

Fixes: #22222
2 files changed