configure: check for EGL header if EGL is required

Change-Id: Id7501b9adcd817ce84bfde3a928fe8b4c7e7e01f
Reviewed-on: https://gerrit.libreoffice.org/52330Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>
(cherry picked from commit e2e31184)
Reviewed-on: https://gerrit.libreoffice.org/52382Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>

configure.ac

@@ -9711,6 +9711,8 @@ if test "x$enable_gtk3" = "xyes"; then
     dnl We require egl only for the gtk3 plugin. Otherwise we use glx.
     if test "$with_system_epoxy" != "yes"; then
         AC_CHECK_LIB(EGL, eglMakeCurrent, [:], AC_MSG_ERROR([libEGL required.]))
+        AC_CHECK_HEADER(EGL/eglplatform.h, [],
+                        [AC_MSG_ERROR(EGL headers not found. install mesa-libEGL-devel)], [])
     fi
 fi
 AC_SUBST(GTK3_LIBS)