In https://crrev.com/c/3764190, V8_COMPILER_IS_MSVC gets used before it
is defined, so it has no effect. Move the V8_COMPILER_IS_MSVC define up
to fix this.

Change-Id: I94c63ad2a8a7555c85730792c1f91e1285a9b77f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3774095
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82090}