Architecture judgement functions like ‘IsMipsArchVariant’, ‘IsFpxxMode’
used to be macro functions, which may cause ‘unreachable-code’ error if
they are used as condition expressions for ‘if’ statements.
This CL change them to constexpr functions to avoid it.

Change-Id: Id3d8473920711a05abc39265c88e91cc1cb7d5e2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2115833
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Auto-Submit: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66843}