[flang][OpenMP] Add test for checking overloaded operator in atomic u…

…pdate (llvm#88471)

Atomic update expression does not allow overloaded user-defined
operators. This PR adds a test case for the same; the semantic check is
already existent.

flang/test/Semantics/OpenMP/atomic-update-overloaded-ops.f90

@@ -0,0 +1,31 @@
+! RUN: %python %S/../test_errors.py %s %flang_fc1 -fopenmp
+
+module new_operator
+ implicit none
+
+ interface operator(.MYOPERATOR.)
+ module procedure myprocedure
+ end interface
+contains
+ pure integer function myprocedure(param1, param2)
+ integer, intent(in) :: param1, param2
+ myprocedure = param1 + param2
+ end function
+end module
+
+program sample
+ use new_operator
+ implicit none
+ integer :: x, y 
+
+ !$omp atomic update
+ x = x / y
+
+ !$omp atomic update
+ !ERROR: Invalid or missing operator in atomic update statement
+ x = x .MYOPERATOR. y
+
+ !$omp atomic
+ !ERROR: Invalid or missing operator in atomic update statement
+ x = x .MYOPERATOR. y
+end program