gcc8,gcc9: fix ctypes on NetBSD

This patch was applied to gcc7 in aab8c7b ("netbsd: add cross target"),
but it hasn't been brought forward to newer compilers that have the
same problem.

GCC 6 and (probably) GCC 4.9 also have the issue, but the patch
doesn't apply cleanly to them so I'm leaving them alone for now.

GCC 10, our current default, appears to have finally fixed this.

pkgs/development/compilers/gcc/8/default.nix

@@ -55,6 +55,7 @@ let majorVersion = "8";
 
     patches =
          optional (targetPlatform != hostPlatform) ../libstdc++-target.patch
+      ++ optional targetPlatform.isNetBSD ../libstdc++-netbsd-ctypes.patch
       ++ optional noSysDirs ../no-sys-dirs.patch
       /* ++ optional (hostPlatform != buildPlatform) (fetchpatch { # XXX: Refine when this should be applied
         url = "https://git.busybox.net/buildroot/plain/package/gcc/${version}/0900-remove-selftests.patch?id=11271540bfe6adafbc133caf6b5b902a816f5f02";

pkgs/development/compilers/gcc/9/default.nix

@@ -70,6 +70,7 @@ let majorVersion = "9";
       # This patch can most likely be removed by a post 9.3.0-release.
       [ ./avoid-cycling-subreg-reloads.patch ]
       ++ optional (targetPlatform != hostPlatform) ../libstdc++-target.patch
+      ++ optional targetPlatform.isNetBSD ../libstdc++-netbsd-ctypes.patch
       ++ optional noSysDirs ../no-sys-dirs.patch
       /* ++ optional (hostPlatform != buildPlatform) (fetchpatch { # XXX: Refine when this should be applied
         url = "https://git.busybox.net/buildroot/plain/package/gcc/${version}/0900-remove-selftests.patch?id=11271540bfe6adafbc133caf6b5b902a816f5f02";