base/debug: 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).

[email protected]

Bug: 1234043
Test: No functionality change
Change-Id: Ibcd0a2fdcedaf19d81f8c4aaf4c136803ca85423
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3390853
Reviewed-by: Nico Weber <[email protected]>
Commit-Queue: Xiaohan Wang <[email protected]>
Cr-Commit-Position: refs/heads/main@{#959654}
diff --git a/base/debug/test_elf_image_builder.cc b/base/debug/test_elf_image_builder.cc
index 108d8d0..5a8dbea 100644
--- a/base/debug/test_elf_image_builder.cc
+++ b/base/debug/test_elf_image_builder.cc
@@ -256,7 +256,7 @@
 
   Dyn* strtab_dyn = reinterpret_cast<Dyn*>(loc);
   strtab_dyn->d_tag = DT_STRTAB;
-#if defined(OS_FUCHSIA) || defined(OS_ANDROID)
+#if BUILDFLAG(IS_FUCHSIA) || BUILDFLAG(IS_ANDROID)
   // Fuchsia and Android do not alter the symtab pointer on ELF load -- it's
   // expected to remain a 'virutal address'.
   strtab_dyn->d_un.d_ptr =