output byref types into --header file [backport: 1.6] (#19505)

* output byref types into --header file

fix #19445

* fix comments

* set targets

compiler/ccgtypes.nim

@@ -471,6 +471,11 @@ proc genProcParams(m: BModule, t: PType, rettype, params: var Rope,
     var arr = t[0]
     if params != nil: params.add(", ")
     if mapReturnType(m.config, t[0]) != ctArray:
+      if isHeaderFile in m.flags:
+        # still generates types for `--header`
+        params.add(getTypeDescAux(m, arr, check, skResult))
+        params.add("*")
+      else:
         params.add(getTypeDescWeak(m, arr, check, skResult))
         params.add("*")
     else:

tests/ccgbugs/m19445.c

@@ -0,0 +1,3 @@
+#include "m19445.h"
+
+const Foo f = {10, 20, 30, 40};

tests/ccgbugs/t19445.nim

@@ -0,0 +1,13 @@
+discard """
+  matrix: "--nimcache:tests/ccgbugs/nimcache19445 --cincludes:nimcache19445 --header:m19445"
+  targets: "c"
+"""
+
+# bug #19445
+type
+  Foo* {.exportc.} = object
+    a*, b*, c*, d*: int
+
+proc dummy(): Foo {.exportc.} = discard
+
+{.compile:"m19445.c".}