[OpenMP] Add directive spellings introduced in spec v6.0

For background information see
https://discourse.llvm.org/t/rfc-alternative-spellings-of-openmp-directives/85507

Author: kparzysz

llvm/include/llvm/Frontend/OpenMP/OMP.td

@@ -677,7 +677,8 @@ def OMP_Cancel : Directive<[Spelling<"cancel">]> {
   let association = AS_None;
   let category = CA_Executable;
 }
-def OMP_CancellationPoint : Directive<[Spelling<"cancellation point">]> {
+def OMP_CancellationPoint : Directive<[Spelling<"cancellation point", 1, 52>,
+                                       Spelling<"cancellation_point", 60>]> {
   let allowedOnceClauses = [
     VersionedClause<OMPC_CancellationConstructType>,
   ];
@@ -691,21 +692,24 @@ def OMP_Critical : Directive<[Spelling<"critical">]> {
   let association = AS_Block;
   let category = CA_Executable;
 }
-def OMP_DeclareMapper : Directive<[Spelling<"declare mapper">]> {
+def OMP_DeclareMapper : Directive<[Spelling<"declare mapper", 1, 52>,
+                                   Spelling<"declare_mapper", 60>]> {
   let requiredClauses = [
     VersionedClause<OMPC_Map, 45>,
   ];
   let association = AS_None;
   let category = CA_Declarative;
 }
-def OMP_DeclareReduction : Directive<[Spelling<"declare reduction">]> {
+def OMP_DeclareReduction : Directive<[Spelling<"declare reduction", 1, 52>,
+                                      Spelling<"declare_reduction", 60>]> {
   let allowedOnceClauses = [
     VersionedClause<OMPC_Initializer>,
   ];
   let association = AS_None;
   let category = CA_Declarative;
 }
-def OMP_DeclareSimd : Directive<[Spelling<"declare simd">]> {
+def OMP_DeclareSimd : Directive<[Spelling<"declare simd", 1, 52>,
+                                 Spelling<"declare_simd", 60>]> {
   let allowedClauses = [
     VersionedClause<OMPC_Aligned>,
     VersionedClause<OMPC_Linear>,
@@ -721,7 +725,8 @@ def OMP_DeclareSimd : Directive<[Spelling<"declare simd">]> {
   let association = AS_Declaration;
   let category = CA_Declarative;
 }
-def OMP_DeclareTarget : Directive<[Spelling<"declare target">]> {
+def OMP_DeclareTarget : Directive<[Spelling<"declare target", 1, 52>,
+                                   Spelling<"declare_target", 60>]> {
   let allowedClauses = [
     VersionedClause<OMPC_Enter, 52>,
     VersionedClause<OMPC_Indirect>,
@@ -734,7 +739,8 @@ def OMP_DeclareTarget : Directive<[Spelling<"declare target">]> {
   let association = AS_None;
   let category = CA_Declarative;
 }
-def OMP_DeclareVariant : Directive<[Spelling<"declare variant">]> {
+def OMP_DeclareVariant : Directive<[Spelling<"declare variant", 1, 52>,
+                                    Spelling<"declare_variant", 60>]> {
   let allowedClauses = [
     VersionedClause<OMPC_AdjustArgs, 51>,
   ];
@@ -1093,7 +1099,8 @@ def OMP_Target : Directive<[Spelling<"target">]> {
   let association = AS_Block;
   let category = CA_Executable;
 }
-def OMP_TargetData : Directive<[Spelling<"target data">]> {
+def OMP_TargetData : Directive<[Spelling<"target data", 1, 52>,
+                                Spelling<"target_data", 60>]> {
   let allowedOnceClauses = [
     VersionedClause<OMPC_Device>,
     VersionedClause<OMPC_If>,
@@ -1106,7 +1113,8 @@ def OMP_TargetData : Directive<[Spelling<"target data">]> {
   let association = AS_Block;
   let category = CA_Executable;
 }
-def OMP_TargetEnterData : Directive<[Spelling<"target enter data">]> {
+def OMP_TargetEnterData : Directive<[Spelling<"target enter data", 1, 52>,
+                                     Spelling<"target_enter_data", 60>]> {
   let allowedClauses = [
     VersionedClause<OMPC_Depend>,
   ];
@@ -1121,7 +1129,8 @@ def OMP_TargetEnterData : Directive<[Spelling<"target enter data">]> {
   let association = AS_None;
   let category = CA_Executable;
 }
-def OMP_TargetExitData : Directive<[Spelling<"target exit data">]> {
+def OMP_TargetExitData : Directive<[Spelling<"target exit data", 1, 52>,
+                                    Spelling<"target_exit_data", 60>]> {
   let allowedClauses = [
     VersionedClause<OMPC_Depend>,
   ];
@@ -1136,7 +1145,8 @@ def OMP_TargetExitData : Directive<[Spelling<"target exit data">]> {
   let association = AS_None;
   let category = CA_Executable;
 }
-def OMP_TargetUpdate : Directive<[Spelling<"target update">]> {
+def OMP_TargetUpdate : Directive<[Spelling<"target update", 1, 52>,
+                                  Spelling<"target_update", 60>]> {
   let allowedClauses = [
     VersionedClause<OMPC_Depend>,
     VersionedClause<OMPC_From>,