iASL: Enhancement for constant folding.

Add support to fold expressions with a target operand -- these are
folded and converted to a Store operator:

Add (4, 3, INT1) --> Store (7, INT1)

Also supports ASL+ constructs:

INT1 = 4 + 3 --> Store (7, INT1)

source/compiler/aslcompile.c

@@ -267,8 +267,16 @@ CmDoCompile (
     Event = UtBeginEvent ("Constant folding via AML interpreter");
     DbgPrint (ASL_DEBUG_OUTPUT,
         "\nInterpreting compile-time constant expressions\n\n");
-    TrWalkParseTree (RootNode, ASL_WALK_VISIT_DOWNWARD,
-        OpcAmlConstantWalk, NULL, NULL);
+
+    if (Gbl_FoldConstants)
+    {
+        TrWalkParseTree (RootNode, ASL_WALK_VISIT_DOWNWARD,
+            OpcAmlConstantWalk, NULL, NULL);
+    }
+    else
+    {
+        DbgPrint (ASL_PARSE_OUTPUT, "    Optional folding disabled\n");
+    }
     UtEndEvent (Event);
 
     /* Update AML opcodes if necessary, after constant folding */

source/compiler/aslcompiler.h

@@ -757,6 +757,10 @@ ACPI_PARSE_OBJECT *
 TrAllocateNode (
     UINT32                  ParseOpcode);
 
+void
+TrPrintNodeCompileFlags (
+    UINT32                  Flags);
+
 void
 TrReleaseNode (
     ACPI_PARSE_OBJECT       *Op);
@@ -776,6 +780,10 @@ ACPI_PARSE_OBJECT *
 TrCreateLeafNode (
     UINT32                  ParseOpcode);
 
+ACPI_PARSE_OBJECT *
+TrCreateNullTarget (
+    void);
+
 ACPI_PARSE_OBJECT *
 TrCreateAssignmentNode (
     ACPI_PARSE_OBJECT       *Target,