Add the ability to pass a value with the -d flag

This allows the end user to use the {.magic: "IntDefine"/"StrDefine"}
pragmas to pass values into code at compile time.  This has a nice side
effect of also allowing/requiring a default value to be assigned in the
code (see osalloc.nim/StandaloneHeapSize for an example)

compiler/wordrecg.nim

@@ -36,6 +36,7 @@ type
     wColon, wColonColon, wEquals, wDot, wDotDot,
     wStar, wMinus,
     wMagic, wThread, wFinal, wProfiler, wObjChecks,
+    wIntDefine, wStrDefine,
 
     wDestroy,
 
@@ -121,7 +122,7 @@ const
 
     ":", "::", "=", ".", "..",
     "*", "-",
-    "magic", "thread", "final", "profiler", "objchecks",
+    "magic", "thread", "final", "profiler", "objchecks", "intdefine", "strdefine",
 
     "destroy",