Revert "Roll Clang from 6d667d4b261e to 7f374b6902fa" (#42896)

Reverts #42718

This is causing a breakage for Fuchsia (see b/286634225)

Author: Casey Hillers

DEPS

@@ -39,7 +39,7 @@ vars = {
   # The list of revisions for these tools comes from Fuchsia, here:
   # https://fuchsia.googlesource.com/integration/+/HEAD/toolchain
   # If there are problems with the toolchain, contact fuchsia-toolchain@.
-  'clang_version': 'git_revision:7f374b6902fad9caed41284a57d573abe9ada9d1',
+  'clang_version': 'git_revision:6d667d4b261e81f325756fdfd5bb43b3b3d2451d',
 
   # The goma version and the clang version can be tightly coupled. If goma
   # stops working on a clang roll, this may need to be updated using the value