databases/mongodb80: unbreak on 15 + llvm 19.1.2

stick to <= llvm18 on FreeBSD 15

fixes:
In file included from src/third_party/mozjs/platform/aarch64/freebsd/build/Unified_cpp_js_src13.cpp:2:
In file included from src/third_party/mozjs/extract/js/src/vm/GlobalObject.cpp:7:
In file included from src/third_party/mozjs/extract/js/src/vm/GlobalObject.h:34:
In file included from src/third_party/mozjs/extract/js/src/vm/JSContext.h:22:
In file included from src/third_party/mozjs/extract/js/src/jit/PcScriptCache.h:12:
In file included from src/third_party/mozjs/extract/js/src/vm/Runtime.h:49:
In file included from src/third_party/mozjs/extract/js/src/vm/Caches.h:17:
In file included from src/third_party/mozjs/extract/js/src/frontend/ScopeBindingCache.h:20:
In file included from src/third_party/mozjs/extract/js/src/vm/Scope.h:34:
In file included from src/third_party/mozjs/extract/js/src/vm/JSFunction.h:25:
In file included from src/third_party/mozjs/extract/js/src/vm/JSScript.h:41:
In file included from src/third_party/mozjs/extract/js/src/vm/SharedImmutableStringsCache.h:22:
src/third_party/mozjs/extract/js/src/threading/ExclusiveData.h:113:29: error: reference to non-static member function must be called
  113 |       : lock_(std::move(rhs.lock)), value_(std::move(rhs.value_)) {
      |                         ~~~~^~~~
1 error generated.