Since inlining budget calculation is fixed in CL 70151
runtime.nextFreeFast is no longer inlineable on MIPS64x because
it does not support Ctz64 as intrinsic. Skip the test.

Updates #22239.

Change-Id: Id00d55628ddb4b48d27aebfa10377a896765d569
Reviewed-on: https://go-review.googlesource.com/72271
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>