games/dangerdeep: Unbreak build on FreeBSD >= 12.1

src/subsim.cpp:1739:2: error: reference to 'thread' is ambiguous
        thread::auto_ptr<music> mmusic(new music(use_sound));
        ^
src/thread.h:37:7: note: candidate found by name lookup is 'thread'
class thread
      ^
/usr/include/c++/v1/__threading_support:397:24: note: candidate found by name lookup is 'std::__1::thread'
class _LIBCPP_TYPE_VIS thread;
                       ^
2 warnings and 1 error generated.

http://beefy6.nyi.freebsd.org/data/121amd64-default/529299/logs/errors/dangerdeep-0.3.0_14.log

games/dangerdeep/files/patch-src__subsim.cpp

@@ -1,6 +1,6 @@
---- ./src/subsim.cpp.orig	2007-06-11 11:16:23.000000000 -0400
-+++ ./src/subsim.cpp	2014-08-11 09:56:15.000000000 -0400
-@@ -31,6 +31,7 @@
+--- src/subsim.cpp.orig	2007-06-11 15:16:23 UTC
++++ src/subsim.cpp
+@@ -31,6 +31,7 @@ Foundation, Inc., 59 Temple Place, Suite 330, Boston, 
  #else
  #include "oglext/OglExt.h"
  #endif
@@ -8,3 +8,12 @@
  #include <glu.h>
  #include <SDL.h>
  #include <SDL_net.h>
+@@ -1735,7 +1736,7 @@ int mymain(list<string>& args)
+ 	glEnable(GL_LIGHT0);
+ 
+ 	// create and start thread for music handling.
+-	thread::auto_ptr<music> mmusic(new music(use_sound));
++	::thread::auto_ptr<music> mmusic(new music(use_sound));
+ 	mmusic->start();
+ 
+ 	reset_loading_screen();

games/dangerdeep/files/patch-src_coastmap.h

@@ -0,0 +1,20 @@
+--- src/coastmap.h.orig	2020-03-29 09:04:12 UTC
++++ src/coastmap.h
+@@ -151,7 +151,7 @@ class coastmap
+ 	void process_coastline(int x, int y);
+ 	void process_segment(int x, int y);
+ 
+-	class worker : public thread
++	class worker : public ::thread
+ 	{
+ 		coastmap& cm;
+ 	public:
+@@ -163,7 +163,7 @@ class coastmap
+ 		}
+ 	};
+ 
+-	thread::auto_ptr<worker> myworker;
++	::thread::auto_ptr<worker> myworker;
+ 	void construction_threaded();
+ 
+ public: