configure: account for CLANG_VENDOR when checking for llvm version

Fixes: #29536

PR-URL: #33860
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: Nathan Blair

configure.py

@@ -794,7 +794,7 @@ def get_nasm_version(asm):
 
 def get_llvm_version(cc):
   return get_version_helper(
-    cc, r"(^(?:FreeBSD )?clang version|based on LLVM) ([0-9]+\.[0-9]+)")
+    cc, r"(^(?:.+ )?clang version|based on LLVM) ([0-9]+\.[0-9]+)")
 
 def get_xcode_version(cc):
   return get_version_helper(