[Flang][OpenMP] : Add a temporary lowering for workshare directive

As a temporary solution, lower workshare to the single directive

Author: kiranchandramohan

flang/lib/Lower/OpenMP.cpp

@@ -3312,7 +3312,11 @@ genOMP(Fortran::lower::AbstractConverter &converter,
                /*outerCombined=*/false);
     break;
   case llvm::omp::Directive::OMPD_workshare:
-    TODO(currentLocation, "Workshare construct");
+    // FIXME: Workshare is not a commonly used OpenMP construct, an
+    // implementation for this feature will come later. For the codes
+    // that use this construct, add a single construct for now.
+    genSingleOp(converter, eval, currentLocation, beginClauseList,
+                endClauseList);
     break;
   default: {
     // Codegen for combined directives

flang/test/Lower/OpenMP/workshare.f90

@@ -0,0 +1,16 @@
+
+!RUN: %flang_fc1 -emit-hlfir -fopenmp %s -o - | FileCheck %s
+
+!CHECK-LABEL: func @_QPsb
+subroutine sb(arr)
+  integer :: arr(:)
+!CHECK: omp.parallel  {
+  !$omp parallel
+!CHECK: omp.single  {
+  !$omp workshare
+    arr = 0
+  !$omp end workshare
+!CHECK: }
+  !$omp end parallel
+!CHECK: }
+end subroutine