Add Intel SIMD vectorization directives to hot-spot functions

Apply Intel Advisor optimization recommendations:
- Add FORCEINLINE to polint for better inlining
- Add SIMD VECTORLENGTHFOR and UNROLL directives to fderivs,
  fdderivs, symmetry_bd, and kodis functions

This improves vectorization efficiency of finite difference
computations.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

AMSS_NCKU_source/kodiss.f90

@@ -65,6 +65,8 @@ real*8,intent(in) :: eps
 !                       dx^4
 
 !  note the sign (-1)^r-1, now r=2
+!DIR$ SIMD VECTORLENGTHFOR(KNOWN_INTEGER=8)
+!DIR$ UNROLL PARTIAL(4)
   do k=1,ex(3)
   do j=1,ex(2)
   do i=1,ex(1)