media: Use BUILDFLAG for OS checking

Use BUILDFLAG(IS_XXX) instead of defined(OS_XXX).

Generated by `os_buildflag_migration.py` (https://crrev.com/c/3311983).

Bug: 1234043
Test: No functionality change
Change-Id: I5f992512001e4e00ff46d534faa9f0217d37a523
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3373744
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Xiaohan Wang <xhwang@chromium.org>
Owners-Override: Xiaohan Wang <xhwang@chromium.org>
Cr-Commit-Position: refs/heads/main@{#959535}
NOKEYCHECK=True
GitOrigin-RevId: d4983e89a3c08a7a597160cff1b15313d5e93bb3
6 files changed