Hi Chau
One more thing,  rcore_drm.c  contains the line:
#include "EGL/egl.h"        // Native platform windowing system interface
If you look in  EGL/egl.h  you'll find it defines  EGL_OPENGL_ES3_BIT:
#ifndef EGL_VERSION_1_5
#define EGL_VERSION_1_5 1
typedef void *EGLSync;
typedef intptr_t EGLAttrib;
typedef khronos_utime_nanoseconds_t EGLTime;
typedef void *EGLImage;
#define EGL_CONTEXT_MAJOR_VERSION         0x3098
#define EGL_CONTEXT_MINOR_VERSION         0x30FB
#define EGL_CONTEXT_OPENGL_PROFILE_MASK   0x30FD
#define EGL_CONTEXT_OPENGL_RESET_NOTIFICATION_STRATEGY 0x31BD
#define EGL_NO_RESET_NOTIFICATION         0x31BE
#define EGL_LOSE_CONTEXT_ON_RESET         0x31BF
#define EGL_CONTEXT_OPENGL_CORE_PROFILE_BIT 0x00000001
#define EGL_CONTEXT_OPENGL_COMPATIBILITY_PROFILE_BIT 0x00000002
#define EGL_CONTEXT_OPENGL_DEBUG          0x31B0
#define EGL_CONTEXT_OPENGL_FORWARD_COMPATIBLE 0x31B1
#define EGL_CONTEXT_OPENGL_ROBUST_ACCESS  0x31B2
#define EGL_OPENGL_ES3_BIT                0x00000040
 ----- Snip -----But it only does that if  EGL_VERSION_1_5  has not already
been defined somewhere else in the build process.