Bracket arguments to tr so they work with Solaris tr

Bracket arguments to tr so they work with Solaris tr

https://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/autoconf-2.69/html_node/Limitations-of-Usual-Tools.html#index-g_t_0040command_007btr_007d-1842

Without this fix, egl fails to build on Solaris, with the error:

<command-line>:0:22: error: '_EGL_PLATFORM_x11' undeclared (first use in this function)
egldisplay.c:207:31: note: in expansion of macro '_EGL_NATIVE_PLATFORM'
             native_platform = _EGL_NATIVE_PLATFORM;
                               ^

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Cc: "10.5" <mesa-stable@lists.freedesktop.org>