[gn build] fix build after a7b2847216

Ports 6e42a417ba since it's now needed, and undo an accidental
deletion from d69762c404 while here (this part is not needed to fix
the build, it's just in the vicinity).

llvm/utils/gn/secondary/llvm/include/llvm/Frontend/OpenACC/BUILD.gn

@@ -6,7 +6,7 @@ tablegen("ACC") {
   output_name = "ACC.h.inc"
 }
 
-tablegen("ACC.cpp") {
+tablegen("ACCcpp") {
   visibility = [ ":acc_gen" ]
   args = [ "-gen-directive-gen" ]
   output_name = "ACC.cpp.inc"
@@ -14,5 +14,8 @@ tablegen("ACC.cpp") {
 }
 
 group("acc_gen") {
-  deps = [ ":ACC" ]
+  deps = [
+    ":ACC",
+    ":ACCcpp",
+  ]
 }

llvm/utils/gn/secondary/llvm/include/llvm/Frontend/OpenMP/BUILD.gn

@@ -6,6 +6,13 @@ tablegen("OMP") {
   output_name = "OMP.h.inc"
 }
 
+tablegen("OMPcpp") {
+  visibility = [ ":public_tablegen" ]
+  args = [ "-gen-directive-gen" ]
+  output_name = "OMP.cpp.inc"
+  td_file = "OMP.td"
+}
+
 # Groups all tablegen() calls that create .inc files that are included in
 # Frontent/OpenMP's public headers (just one so far).
 # //llvm/lib/Frontend/OpenMP has this as a public_dep, so targets depending on
@@ -14,5 +21,6 @@ group("public_tablegen") {
   public_deps = [
     # Frontend/OpenMP's public headers include OMP.h.inc.
     ":OMP",
+    ":OMPcpp",
   ]
 }