Bug 1901895 - Upgrade clang 18 toolchain to 18.1.7. r=firefox-build-system-reviewers,sergesanspaille

Differential Revision: https://phabricator.services.mozilla.com/D213346

taskcluster/kinds/fetch/toolchains.yml

@@ -362,11 +362,11 @@ clang-17:
         revision: 6009708b4367171ccdbf4b5905cb6a803753fe18
 
 clang-18:
-    description: clang 18.1.5 source code
+    description: clang 18.1.7 source code
     fetch:
         type: git
         repo: https://github.com/llvm/llvm-project
-        revision: 617a15a9eac96088ae5e9134248d8236e34b91b1
+        revision: 768118d1ad38bf13c545828f67bd6b474d61fc55
 
 clang-trunk:
     description: clang main branch source code