egl: add HAVE_LIBDRM define, fix EGL X11 platform

Commit a594cec broke EGL X11 backend by adding dependency between
X11 and DRM backends requiring HAVE_EGL_PLATFORM_DRM defined for X11.

This patch fixes the issue by adding additional define for libdrm
detection independent of which backend is being compiled. Tested by
compiling Mesa with '--with-egl-platforms=x11' and running es2gears_x11
+ glbenchmark2.7 successfully.

v2: return true for dri2_auth if running without libdrm (Samuel)
v3: check libdrm when building EGL drm platform + AM_CFLAGS fix (Emil)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=72062
Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>
Cc: Samuel Thibault <samuel.thibault@ens-lyon.org>
Cc: mesa-stable@lists.freedesktop.org

configure.ac

@@ -761,6 +761,9 @@ AC_SUBST([MESA_LLVM])
 # Check for libdrm
 PKG_CHECK_MODULES([LIBDRM], [libdrm >= $LIBDRM_REQUIRED],
                   [have_libdrm=yes], [have_libdrm=no])
+if test "x$have_libdrm" = xyes; then
+	DEFINES="$DEFINES -DHAVE_LIBDRM"
+fi
 
 PKG_CHECK_MODULES([LIBUDEV], [libudev >= $LIBUDEV_REQUIRED],
                   have_libudev=yes, have_libudev=no)
@@ -1439,6 +1442,8 @@ for plat in $egl_platforms; do
 	drm)
 		test "x$enable_gbm" = "xno" &&
 			AC_MSG_ERROR([EGL platform drm needs gbm])
+		test "x$have_libdrm" != xyes &&
+			AC_MSG_ERROR([EGL platform drm requires libdrm >= $LIBDRM_REQUIRED])
 		;;
 
 	android|fbdev|gdi|null)

src/egl/drivers/dri2/platform_x11.c

@@ -33,7 +33,7 @@
 #include <fcntl.h>
 #include <errno.h>
 #include <unistd.h>
-#ifdef HAVE_DRM_PLATFORM
+#ifdef HAVE_LIBDRM
 #include <xf86drm.h>
 #endif
 #include <sys/types.h>
@@ -608,7 +608,7 @@ dri2_x11_authenticate(_EGLDisplay *disp, uint32_t id)
 static EGLBoolean
 dri2_authenticate(_EGLDisplay *disp)
 {
-#ifdef HAVE_DRM_PLATFORM
+#ifdef HAVE_LIBDRM
    struct dri2_egl_display *dri2_dpy = dri2_egl_display(disp);
    drm_magic_t magic;
 
@@ -621,11 +621,8 @@ dri2_authenticate(_EGLDisplay *disp)
       _eglLog(_EGL_WARNING, "DRI2: failed to authenticate");
       return EGL_FALSE;
    }
-
-   return EGL_TRUE;
-#else
-   return EGL_FALSE;
 #endif
+   return EGL_TRUE;
 }
 
 static EGLBoolean