Merge pull request #993 from kcbanner/gl_funcs_ext

Allow extensions to load additional GL functions via SG_GL_FUNCS_EXT

sokol_gfx.h

@@ -6540,8 +6540,13 @@ _SOKOL_PRIVATE void _sg_dummy_update_image(_sg_image_t* img, const sg_image_data
 // optional GL loader for win32
 #if defined(_SOKOL_USE_WIN32_GL_LOADER)
 
+#ifndef SG_GL_FUNCS_EXT
+#define SG_GL_FUNCS_EXT
+#endif
+
 // X Macro list of GL function names and signatures
 #define _SG_GL_FUNCS \
+    SG_GL_FUNCS_EXT \
     _SG_XMACRO(glBindVertexArray,                 void, (GLuint array)) \
     _SG_XMACRO(glFramebufferTextureLayer,         void, (GLenum target, GLenum attachment, GLuint texture, GLint level, GLint layer)) \
     _SG_XMACRO(glGenFramebuffers,                 void, (GLsizei n, GLuint * framebuffers)) \