[mlir][OpenMP] Use correct debug location with link clause. (llvm#145026)

Please see the following program.

```
module test_0
    INTEGER :: sp = 1
!$omp declare target link(sp)
end module test_0

program main
use test_0
integer :: new_len

!$omp target map(tofrom:new_len) map(tofrom:sp)
    new_len = sp
!$omp end target

  print *, new_len
  print *, sp
end program
```

When compiled with
`flang -g -O0 -fopenmp --offload-arch=gfx1100`

will fail the compilation with the following error:

`dbg attachment points at wrong subprogram for function`

The reason is that with the `link` clause on `!$omp declare target`, an
extra load instruction is inserted. But the debug location was not
updated before insertion which caused an invalid location to be attached
to the instruction.

Author: abidh

mlir/lib/Target/LLVMIR/Dialect/OpenMP/OpenMPToLLVMIRTranslation.cpp

@@ -4831,6 +4831,7 @@ handleDeclareTargetMapVar(MapInfoData &mapData,
                           llvm::IRBuilderBase &builder, llvm::Function *func) {
   assert(moduleTranslation.getOpenMPBuilder()->Config.isTargetDevice() &&
          "function only supported for target device codegen");
+  llvm::IRBuilderBase::InsertPointGuard guard(builder);
   for (size_t i = 0; i < mapData.MapClause.size(); ++i) {
     // In the case of declare target mapped variables, the basePointer is
     // the reference pointer generated by the convertDeclareTargetAttr
@@ -4865,6 +4866,7 @@ handleDeclareTargetMapVar(MapInfoData &mapData,
       for (llvm::User *user : userVec) {
         if (auto *insn = dyn_cast<llvm::Instruction>(user)) {
           if (insn->getFunction() == func) {
+            builder.SetCurrentDebugLocation(insn->getDebugLoc());
             auto *load = builder.CreateLoad(mapData.BasePointers[i]->getType(),
                                             mapData.BasePointers[i]);
             load->moveBefore(insn->getIterator());

mlir/test/Target/LLVMIR/omptarget-debug-map-link-loc.mlir

@@ -0,0 +1,40 @@
+// RUN: mlir-translate -mlir-to-llvmir %s
+
+module attributes {dlti.dl_spec = #dlti.dl_spec<#dlti.dl_entry<"dlti.alloca_memory_space", 5 : ui32>>, llvm.target_triple = "amdgcn-amd-amdhsa", omp.is_target_device = true} {
+  llvm.mlir.global external @_QMtest_0Esp() {addr_space = 1 : i32, omp.declare_target = #omp.declaretarget<device_type = (any), capture_clause = (link)>} : i32 {
+    %0 = llvm.mlir.constant(1 : i32) : i32 loc(#loc1)
+    llvm.return %0 : i32 loc(#loc1)
+  } loc(#loc1)
+  llvm.func @_QQmain() {
+    %0 = llvm.mlir.constant(1 : i64) : i64
+    %1 = llvm.alloca %0 x i32 : (i64) -> !llvm.ptr<5> loc(#loc2)
+    %2 = llvm.addrspacecast %1 : !llvm.ptr<5> to !llvm.ptr loc(#loc2)
+    %5 = llvm.mlir.addressof @_QMtest_0Esp : !llvm.ptr<1> loc(#loc1)
+    %6 = llvm.addrspacecast %5 : !llvm.ptr<1> to !llvm.ptr loc(#loc1)
+    %7 = omp.map.info var_ptr(%2 : !llvm.ptr, i32) map_clauses(tofrom) capture(ByRef) -> !llvm.ptr loc(#loc3)
+    %8 = omp.map.info var_ptr(%6 : !llvm.ptr, i32) map_clauses(tofrom) capture(ByRef) -> !llvm.ptr loc(#loc3)
+    omp.target map_entries(%7 -> %arg0, %8 -> %arg1 : !llvm.ptr, !llvm.ptr) {
+      %16 = llvm.load %arg1 : !llvm.ptr -> i32 loc(#loc5)
+      llvm.store %16, %arg0 : i32, !llvm.ptr loc(#loc5)
+      omp.terminator loc(#loc5)
+    } loc(#loc5)
+    llvm.return loc(#loc6)
+  } loc(#loc15)
+}
+#di_file = #llvm.di_file<"target7.f90" in "">
+#di_null_type = #llvm.di_null_type
+#di_compile_unit = #llvm.di_compile_unit<id = distinct[0]<>,
+ sourceLanguage = DW_LANG_Fortran95, file = #di_file, producer = "flang",
+ isOptimized = false, emissionKind = LineTablesOnly>
+#di_subroutine_type = #llvm.di_subroutine_type<
+  callingConvention = DW_CC_program, types = #di_null_type>
+#di_subprogram = #llvm.di_subprogram<id = distinct[1]<>,
+  compileUnit = #di_compile_unit, scope = #di_file, name = "main",
+  file = #di_file, subprogramFlags = "Definition|MainSubprogram",
+  type = #di_subroutine_type>
+#loc1 = loc("test.f90":3:18)
+#loc2 = loc("test.f90":7:7)
+#loc3 = loc("test.f90":9:18)
+#loc5 = loc("test.f90":11:7)
+#loc6 = loc("test.f90":12:7)
+#loc15 = loc(fused<#di_subprogram>[#loc2])