implement sizeof and alignof operator (manually squashed #5664) (#9356)

compiler/pragmas.nim

@@ -803,9 +803,11 @@ proc singlePragma(c: PContext, sym: PSym, n: PNode, i: var int,
         if sym.typ == nil: invalidPragma(c, it)
         var size = expectIntLit(c, it)
         if not isPowerOfTwo(size) or size <= 0 or size > 8:
-          localError(c.config, it.info, "power of two expected")
+          localError(c.config, it.info, "size may only be 1, 2, 4 or 8")
         else:
           sym.typ.size = size
+          # TODO, this is not correct
+          sym.typ.align = int16(size)
       of wNodecl:
         noVal(c, it)
         incl(sym.loc.flags, lfNoDecl)