Skip compiler directives between OMP PARALLEL DO and the loop (#81021)

This fixes a compilation error when code like this is presented to the
compiler:

  !$OMP PARALLEL DO
  !DIR$ VECTOR ALIGNED
  DO 20 i=1,N
     a = a + 0.5
20   CONTINUE

The directive itself is later ignored (with a warning that this is
happening), but because the compiler already errored out before that
point, it completely fails to compile this code. Other compilers accept
the code without complaints.