[NFC][Flang][Test] Add some missing tests (llvm#110468)

- At most one Collapse clause in SIMD construct
- A DO loop must follow the SIMD directive

Author: Thirumalai-Shaktivel

flang/test/Semantics/OpenMP/do-collapse.f90

@@ -30,5 +30,11 @@ program omp_doCollapse
       do
       end do
     end do
-end program omp_doCollapse
 
+  !ERROR: At most one COLLAPSE clause can appear on the SIMD directive
+  !$omp simd collapse(2) collapse(1)
+  do i = 1, 4
+    j = j + i + 1
+  end do
+  !$omp end simd
+end program omp_doCollapse

flang/test/Semantics/OpenMP/loop-association.f90

@@ -131,4 +131,10 @@
   !$omp end parallel do simd
   !ERROR: The END PARALLEL DO SIMD directive must follow the DO loop associated with the loop construct
   !$omp end parallel do simd
+
+  !ERROR: A DO loop must follow the SIMD directive
+  !$omp simd
+    a = i + 1
+  !ERROR: The END SIMD directive must follow the DO loop associated with the loop construct
+  !$omp end simd
 end