181052 – [patch] make lang/lua not hang on thread creation

no flags

Currently lang/lua links the 'lua' binary without -pthread flag;
this results in any call to 'pthread_create' to completely hang
the program.

Normally this wouldn't be an issue, since Lua doesn't use any
threading functions, but the problem propagates to all the C
extensions as well. For example, if you'll install devel/lgi
(the GObject/Gtk bindings), and try this simple program:

    $ lua-5.1
    Lua 5.1.5  Copyright (C) 1994-2012 Lua.org, PUC-Rio
    > lgi = require 'lgi'
    > gtk = lgi.Gtk
    > gtk.FileChooserDialog {}

.. it will hang at this point. The reason being that Gtk uses
threads internally and tries to spawn a few when you create a
FileChooser object.

That is to say, this problem makes lang/lgi basically unusable,
and prevents any kind of Lua Gtk programs working on FreeBSD.

More directly, you can create an extension that calls
'pthread_create':

    $ cat >test.c <<'EOF'
    #include <lauxlib.h>
    #include <lua.h>
    #include <pthread.h>
    #include <stdio.h>

    static void *
    thread_func(void *arg)
    {
        pthread_exit(0);
    }

    static int
    test(lua_State *L)
    {
        pthread_t thread;
        printf("PTHREAD CREATE\n");
        pthread_create(&thread, NULL, thread_func, NULL);
        printf("PTHREAD JOIN\n");
        pthread_join(thread, NULL);
        printf("DONE\n");
    }

    static const struct luaL_Reg lib[] = {
        {"test", test},
        {NULL, NULL}
    };

    LUALIB_API int
    luaopen_test(lua_State *L)
    {
    #if LUA_VERSION_NUM < 502
        luaL_register(L, "test", lib);
    #else
        luaL_newlib(L, lib);
    #endif
        return 1;
    }
    EOF

    $ cc -I/usr/local/include/lua51 -shared -pthread -fPIC -o test.so test.c

    $ lua-5.1
    Lua 5.1.5  Copyright (C) 1994-2012 Lua.org, PUC-Rio
    > test = require "test"
    > test.test()
    PTHREAD CREATE

.. and again, it hangs.

Fix: See the attached patch. With it both 'lua' and 'lua.so' link
with -pthread.

Note that lang/lua52 and lang/luajit are affected too, but this
PR only deals with lang/lua.

Patch attached with submission follows: