make tests green again

lib/system/dyncalls.nim

@@ -29,7 +29,7 @@ proc nimLoadLibraryError(path: string) =
   stderr.rawWrite("could not load: ")
   stderr.rawWrite(path)
   stderr.rawWrite("\n")
-  when not(defined(nimDebugDlOpen)):
+  when not defined(nimDebugDlOpen) and not defined(windows):
     stderr.rawWrite("compile with -d:nimDebugDlOpen for more information\n")
   quit(1)
 

lib/system/sysio.nim

@@ -37,6 +37,10 @@ proc c_clearerr(f: File) {.
 proc c_feof(f: File): cint {.
   importc: "feof", header: "<stdio.h>".}
 
+when not declared(c_fwrite):
+  proc c_fwrite(buf: pointer, size, n: csize, f: File): cint {.
+    importc: "fwrite", header: "<stdio.h>".}
+
 # C routine that is used here:
 proc c_fread(buf: pointer, size, n: csize, f: File): csize {.
   importc: "fread", header: "<stdio.h>", tags: [ReadIOEffect].}