configuration updates for dlopen:

- cmake, configure (CheckDLOPEN): --enable-sdl-dlopen is now history..
  detach the dl api discovery from SDL_LOADSO_DLOPEN functionality.
  define HAVE_DLOPEN. also define DYNAPI_NEEDS_DLOPEN (CheckDLOPEN is
  called only for relevant platforms.)
- update SDL_config.in and SDL_config.cmake accordingly.
- SDL_dynapi.h: set SDL_DYNAMIC_API to 0 if DYNAPI_NEEDS_DLOPEN is
  defined, but HAVE_DLOPEN is not.
- pthread/SDL_systhread.c: conditionalize dl api use to HAVE_DLOPEN
- SDL_x11opengl.c, SDL_DirectFB_opengl.c, SDL_naclopengles.c: rely
  on HAVE_DLOPEN, not SDL_LOADSO_DLOPEN.
- SDL_config_android.h, SDL_config_iphoneos.h, SDL_config_macosx.h,
  SDL_config_pandora.h, and SDL_config_wiz.h: define HAVE_DLOPEN.

Closes: https://github.com/libsdl-org/SDL/pull/4351

src/dynapi/SDL_dynapi.h

@@ -59,6 +59,8 @@
 #define SDL_DYNAMIC_API 0  /* Turn off for static analysis, so reports are more clear. */
 #elif defined(__VITA__)
 #define SDL_DYNAMIC_API 0  /* vitasdk doesn't support dynamic linking */
+#elif defined(DYNAPI_NEEDS_DLOPEN) && !defined(HAVE_DLOPEN)
+#define SDL_DYNAMIC_API 0  /* we need dlopen(), but don't have it.... */
 #endif
 
 /* everyone else. This is where we turn on the API if nothing forced it off. */

src/thread/pthread/SDL_systhread.c

@@ -41,7 +41,7 @@
 #include "../../core/linux/SDL_dbus.h"
 #endif /* __LINUX__ */
 
-#if defined(__LINUX__) || defined(__MACOSX__) || defined(__IPHONEOS__)
+#if (defined(__LINUX__) || defined(__MACOSX__) || defined(__IPHONEOS__)) && defined(HAVE_DLOPEN)
 #include <dlfcn.h>
 #ifndef RTLD_DEFAULT
 #define RTLD_DEFAULT NULL
@@ -78,10 +78,10 @@ RunThread(void *data)
     return NULL;
 }
 
-#if defined(__MACOSX__) || defined(__IPHONEOS__)
+#if (defined(__MACOSX__) || defined(__IPHONEOS__)) && defined(HAVE_DLOPEN)
 static SDL_bool checked_setname = SDL_FALSE;
 static int (*ppthread_setname_np)(const char*) = NULL;
-#elif defined(__LINUX__)
+#elif defined(__LINUX__) && defined(HAVE_DLOPEN)
 static SDL_bool checked_setname = SDL_FALSE;
 static int (*ppthread_setname_np)(pthread_t, const char*) = NULL;
 #endif
@@ -91,7 +91,7 @@ SDL_SYS_CreateThread(SDL_Thread * thread)
     pthread_attr_t type;
 
     /* do this here before any threads exist, so there's no race condition. */
-    #if defined(__MACOSX__) || defined(__IPHONEOS__) || defined(__LINUX__)
+    #if (defined(__MACOSX__) || defined(__IPHONEOS__) || defined(__LINUX__)) && defined(HAVE_DLOPEN)
     if (!checked_setname) {
         void *fn = dlsym(RTLD_DEFAULT, "pthread_setname_np");
         #if defined(__MACOSX__) || defined(__IPHONEOS__)
@@ -131,7 +131,7 @@ SDL_SYS_SetupThread(const char *name)
 #endif /* !__NACL__ */
 
     if (name != NULL) {
-        #if defined(__MACOSX__) || defined(__IPHONEOS__) || defined(__LINUX__)
+        #if (defined(__MACOSX__) || defined(__IPHONEOS__) || defined(__LINUX__)) && defined(HAVE_DLOPEN)
         SDL_assert(checked_setname);
         if (ppthread_setname_np != NULL) {
             #if defined(__MACOSX__) || defined(__IPHONEOS__)

src/video/directfb/SDL_DirectFB_opengl.c

@@ -47,7 +47,7 @@ struct SDL_GLDriverData
 };
 
 #define OPENGL_REQUIRS_DLOPEN
-#if defined(OPENGL_REQUIRS_DLOPEN) && defined(SDL_LOADSO_DLOPEN)
+#if defined(OPENGL_REQUIRS_DLOPEN) && defined(HAVE_DLOPEN)
 #include <dlfcn.h>
 #define GL_LoadObject(X)    dlopen(X, (RTLD_NOW|RTLD_GLOBAL))
 #define GL_LoadFunction     dlsym

src/video/nacl/SDL_naclopengles.c

@@ -27,7 +27,7 @@
 #include "SDL_video.h"
 #include "SDL_naclvideo.h"
 
-#if SDL_LOADSO_DLOPEN
+#ifdef HAVE_DLOPEN
 #include "dlfcn.h"
 #endif
 
@@ -45,7 +45,7 @@ NACL_GLES_LoadLibrary(_THIS, const char *path)
 void *
 NACL_GLES_GetProcAddress(_THIS, const char *proc)
 {
-#if SDL_LOADSO_DLOPEN
+#ifdef HAVE_DLOPEN
     return dlsym( 0 /* RTLD_DEFAULT */, proc);
 #else
     return NULL;

src/video/x11/SDL_x11opengl.c

@@ -142,7 +142,7 @@ typedef GLXContext(*PFNGLXCREATECONTEXTATTRIBSARBPROC) (Display * dpy,
 #endif
 
 #define OPENGL_REQUIRES_DLOPEN
-#if defined(OPENGL_REQUIRES_DLOPEN) && defined(SDL_LOADSO_DLOPEN)
+#if defined(OPENGL_REQUIRES_DLOPEN) && defined(HAVE_DLOPEN)
 #include <dlfcn.h>
 #define GL_LoadObject(X)    dlopen(X, (RTLD_NOW|RTLD_GLOBAL))
 #define GL_LoadFunction     dlsym
@@ -174,7 +174,7 @@ X11_GL_LoadLibrary(_THIS, const char *path)
     }
     _this->gl_config.dll_handle = GL_LoadObject(path);
     if (!_this->gl_config.dll_handle) {
-#if defined(OPENGL_REQUIRES_DLOPEN) && defined(SDL_LOADSO_DLOPEN)
+#if defined(OPENGL_REQUIRES_DLOPEN) && defined(HAVE_DLOPEN)
         SDL_SetError("Failed loading %s: %s", path, dlerror());
 #endif
         return -1;