adds support for noDecl in constructor (#22811)

Notice the test wouldnt link before

compiler/ccgtypes.nim

@@ -757,6 +757,7 @@ proc getRecordFields(m: BModule; typ: PType, check: var IntSet): Rope =
         isCtorGen = true
         if prc.typ.n.len == 1:
           isDefaultCtorGen = true
+      if lfNoDecl in prc.loc.flags: continue
       genMemberProcHeader(m, prc, header, false, true)
       result.addf "$1;$n", [header]
     if isCtorGen and not isDefaultCtorGen:

doc/manual_experimental.md

@@ -2345,7 +2345,7 @@ proc makeFoo(x: int32): Foo {.constructor.} =
   result.x = x
 ```
 
-It forward declares the constructor in the type definition. When the constructor has parameters, it also generates a default constructor.
+It forward declares the constructor in the type definition. When the constructor has parameters, it also generates a default constructor. One can avoid this behaviour by using `noDecl` in a default constructor.
 
 Like `virtual`, `constructor` also supports a syntax that allows to express C++ constraints.
 

tests/cpp/tconstructor.nim

@@ -16,6 +16,7 @@ ___
 777
 10
 123
+()
 '''
 """
 
@@ -106,4 +107,12 @@ proc init =
     n.x = 123
     echo n.x
 
-init()
+init()
+
+#tests that the ctor is not declared with nodecl. 
+#nodelc also prevents the creation of a default one when another is created.
+type Foo {.exportc.} = object
+
+proc makeFoo(): Foo {.used, constructor, nodecl.} = discard
+
+echo $Foo()