bitsize respected in size calculation. (#9756)

compiler/pragmas.nim

@@ -1062,6 +1062,8 @@ proc singlePragma(c: PContext, sym: PSym, n: PNode, i: var int,
           invalidPragma(c, it)
         else:
           sym.bitsize = expectIntLit(c, it)
+          if sym.bitsize <= 0:
+            localError(c.config, it.info, "bitsize needs to be positive")
       of wGuard:
         if sym == nil or sym.kind notin {skVar, skLet, skField}:
           invalidPragma(c, it)

compiler/sizealignoffsetimpl.nim

@@ -127,9 +127,14 @@ proc computeObjectOffsetsFoldFunction(conf: ConfigRef; n: PNode, initialOffset:
       result.offset = align(offset, result.align)
 
   of nkSym:
-    computeSizeAlign(conf, n.sym.typ)
-    let size = n.sym.typ.size
-    let align = n.sym.typ.align
+    var size = szUnknownSize
+    var align = szUnknownSize
+
+    if n.sym.bitsize == 0: # 0 represents bitsize not set
+      computeSizeAlign(conf, n.sym.typ)
+      size = n.sym.typ.size.int
+      align = n.sym.typ.align.int
+
     result.align = align
     if initialOffset == szUnknownSize or size == szUnknownSize:
       n.sym.offset = szUnknownSize