Replace USE_X11 macro with ENABLE_EGL_X11.

If x11 support is enabled, then the meson and configure scripts will set
a macro named ENABLE_EGL_X11 instead of USE_X11.

USE_X11 will also select the Xlib typedef of EGLNativeDisplayType in
eglplatform.h, and libglvnd does not need or want those.

Enabling or disabling X11 support for EGL only affects platform
detection in eglGetDisplay. The rest of libEGL is supposed to treat
EGLNativeDisplayType as an opaque void* pointer.

configure.ac

@@ -203,7 +203,7 @@ AX_PTHREAD()
 
 if test "x$enable_x11" = "xyes" ; then
     PKG_CHECK_MODULES([X11], [x11])
-    AC_DEFINE([USE_X11], 1,
+    AC_DEFINE([ENABLE_EGL_X11], 1,
         [Define to 1 if X11 support is enabled.])
 fi
 if test "x$enable_glx" = "xyes" ; then

meson.build

@@ -95,7 +95,7 @@ endif
 
 dep_x11_headers = dep_x11.partial_dependency(compile_args : true, includes : true)
 if dep_x11.found()
-  add_project_arguments('-DUSE_X11', language : ['c'])
+  add_project_arguments('-DENABLE_EGL_X11', language : ['c'])
 endif
 
 dep_xext = dep_null

src/EGL/libegl.c

@@ -32,7 +32,7 @@
 #include <unistd.h>
 #include <sys/mman.h>
 
-#if defined(USE_X11)
+#if defined(ENABLE_EGL_X11)
 #include <X11/Xlib.h>
 #endif
 
@@ -176,7 +176,7 @@ static EGLBoolean IsGbmDisplay(void *native_display)
 
 static EGLBoolean IsX11Display(void *dpy)
 {
-#if defined(USE_X11)
+#if defined(ENABLE_EGL_X11)
     void *alloc;
     void *handle;
     void *XAllocID = NULL;
@@ -193,9 +193,9 @@ static EGLBoolean IsX11Display(void *dpy)
     }
 
     return (XAllocID != NULL && XAllocID == alloc);
-#else // defined(USE_X11)
+#else // defined(ENABLE_EGL_X11)
     return EGL_FALSE;
-#endif // defined(USE_X11)
+#endif // defined(ENABLE_EGL_X11)
 }
 
 static EGLBoolean IsWaylandDisplay(void *native_display)