Add epoxy_has_egl()

Similar to `epoxy_has_glx()`, but for the EGL windowing system API.

include/epoxy/egl.h

@@ -47,6 +47,7 @@ EPOXY_BEGIN_DECLS
 
 EPOXY_PUBLIC bool epoxy_has_egl_extension(EGLDisplay dpy, const char *extension);
 EPOXY_PUBLIC int epoxy_egl_version(EGLDisplay dpy);
+EPOXY_PUBLIC bool epoxy_has_egl(void);
 
 EPOXY_END_DECLS
 

src/dispatch_egl.c

@@ -92,3 +92,24 @@ epoxy_has_egl_extension(EGLDisplay dpy, const char *ext)
 {
     return epoxy_extension_in_string(eglQueryString(dpy, EGL_EXTENSIONS), ext) || epoxy_extension_in_string(eglQueryString(NULL, EGL_EXTENSIONS), ext);
 }
+
+/**
+ * @brief Checks whether EGL is available.
+ *
+ * @return `true` if EGL is available
+ */
+bool
+epoxy_has_egl(void)
+{
+#if !PLATFORM_HAS_EGL
+    return false;
+#else
+    EGLDisplay* (* pf_eglGetCurrentDisplay) (void);
+
+    pf_eglGetCurrentDisplay = epoxy_conservative_egl_dlsym("eglGetCurrentDisplay", false);
+    if (pf_eglGetCurrentDisplay)
+        return true;
+
+    return false;
+#endif /* PLATFORM_HAS_EGL */
+}