configure: add mips64el to valid_arch

PR-URL: #13620
Fixes: #13616
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

configure

@@ -47,8 +47,8 @@ parser = optparse.OptionParser()
 
 valid_os = ('win', 'mac', 'solaris', 'freebsd', 'openbsd', 'linux',
             'android', 'aix')
-valid_arch = ('arm', 'arm64', 'ia32', 'mips', 'mipsel', 'ppc', 'ppc64', 'x32',
-              'x64', 'x86', 's390', 's390x')
+valid_arch = ('arm', 'arm64', 'ia32', 'mips', 'mipsel', 'mips64el', 'ppc',
+              'ppc64', 'x32','x64', 'x86', 's390', 's390x')
 valid_arm_float_abi = ('soft', 'softfp', 'hard')
 valid_arm_fpu = ('vfp', 'vfpv3', 'vfpv3-d16', 'neon')
 valid_mips_arch = ('loongson', 'r1', 'r2', 'r6', 'rx')