Clang: the tip-of-tree version is now 12.0.0

Bug: 1105518
Change-Id: I267708d4990adbbdb7d9fe3642fb40d077cad7f8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2297525
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#788567}
GitOrigin-RevId: 1ab49a3f60c5fb12baeddead7cfa583bfabba1d3
diff --git a/toolchain.gni b/toolchain.gni
index 80c2e7b..c7e7656 100644
--- a/toolchain.gni
+++ b/toolchain.gni
@@ -39,7 +39,12 @@
 
 declare_args() {
   # Clang compiler version. Clang files are placed at version-dependent paths.
-  clang_version = "11.0.0"
+  if (llvm_force_head_revision) {
+    clang_version = "12.0.0"
+  } else {
+    # TODO(crbug.com/1105518): Remove in the next Clang roll.
+    clang_version = "11.0.0"
+  }
 }
 
 # Check target_os here instead of is_ios as this file is loaded for secondary