Support Intel ifx compiler

[rouson]

The command

fpm test --compiler ifx

yields the following trailing output:

julienne_test_description_s.f90        failed.
[ 59%] Compiling...
././src/julienne/julienne_test_description_s.f90(25): error #7137: Any procedure referenced in a PURE procedure, including one referenced via a defined operation or assignment, must have an explicit interface and be declared PURE.   [TEST_FUNCTION_]
      lhs_eq_rhs = (lhs%description_ == rhs%description_) .and. associated(lhs%test_function_, rhs%test_function_)
-------------------------------------------------------------------------------^
././src/julienne/julienne_test_description_s.f90(28): catastrophic error: Too many errors, exiting
compilation aborted for ././src/julienne/julienne_test_description_s.f90 (code 1)
<ERROR> Compilation failed for object " src_julienne_julienne_test_description_s.f90.o "
<ERROR> stopping due to failed compilation
STOP 1

[rouson]

This has been reported to Intel as a compiler bug.