internal/gl: use dlsym(3) to load ES 3 symbols

There was a special case for optional symbols for macOS/iOS. It turns out
dlsym(3) works as expected, so this change deletes the special case.

The change is required to make Gio work with ANGLE, which emulates
OpenGL ES on top of Metal.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

internal/gl/gl_unix.go

@@ -25,6 +25,8 @@ import (
 #cgo darwin,ios LDFLAGS: -framework OpenGLES
 
 #include <stdlib.h>
+#define __USE_GNU
+#include <dlfcn.h>
 
 #ifdef __APPLE__
 	#include "TargetConditionals.h"
@@ -34,8 +36,6 @@ import (
 	#include <OpenGL/gl3.h>
 	#endif
 #else
-#define __USE_GNU
-#include <dlfcn.h>
 #include <GLES2/gl2.h>
 #include <GLES3/gl3.h>
 #endif
@@ -144,23 +144,9 @@ __attribute__ ((visibility ("hidden"))) void gio_glBlitFramebuffer(GLint srcX0,
 }
 
 __attribute__((constructor)) static void gio_loadGLFunctions() {
-#ifdef __APPLE__
-	#if TARGET_OS_IPHONE
-	_glInvalidateFramebuffer = glInvalidateFramebuffer;
-	_glBeginQuery = glBeginQuery;
-	_glDeleteQueries = glDeleteQueries;
-	_glEndQuery = glEndQuery;
-	_glGenQueries = glGenQueries;
-	_glGetQueryObjectuiv = glGetQueryObjectuiv;
-	_glTexStorage2D = glTexStorage2D;
-	#endif
-	_glBindBufferBase = glBindBufferBase;
-	_glGetUniformBlockIndex = glGetUniformBlockIndex;
-	_glUniformBlockBinding = glUniformBlockBinding;
-	_glGetStringi = glGetStringi;
-#else
 	// Load libGLESv3 if available.
 	dlopen("libGLESv3.so", RTLD_NOW | RTLD_GLOBAL);
+
 	_glBindBufferBase = dlsym(RTLD_DEFAULT, "glBindBufferBase");
 	_glGetUniformBlockIndex = dlsym(RTLD_DEFAULT, "glGetUniformBlockIndex");
 	_glUniformBlockBinding = dlsym(RTLD_DEFAULT, "glUniformBlockBinding");
@@ -194,7 +180,6 @@ __attribute__((constructor)) static void gio_loadGLFunctions() {
 	_glBindImageTexture = dlsym(RTLD_DEFAULT, "glBindImageTexture");
 	_glTexStorage2D = dlsym(RTLD_DEFAULT, "glTexStorage2D");
 	_glBlitFramebuffer = dlsym(RTLD_DEFAULT, "glBlitFramebuffer");
-#endif
 }
 */
 import "C"