Fix MSVC C4864 warning and testlib message_impl link error

src/snmalloc/mem/corealloc.h

@@ -656,7 +656,8 @@ namespace snmalloc
           smallsizeclass_t sizeclass,
           freelist::Iter<>* fl,
           size_t size) SNMALLOC_FAST_PATH_LAMBDA {
-          return alloc->small_refill<Conts, CheckInit>(sizeclass, *fl, size);
+          return alloc->template small_refill<Conts, CheckInit>(
+            sizeclass, *fl, size);
         },
         this,
         sizeclass,
@@ -693,7 +694,7 @@ namespace snmalloc
         // Deal with alloc zero of with a small object here.
         // Alternative semantics giving nullptr is also allowed by the
         // standard.
-        return self->small_alloc<Conts, CheckInit>(1);
+        return self->template small_alloc<Conts, CheckInit>(1);
       }
 
       return self->template handle_message_queue<noexcept(Conts::failure(0))>(
@@ -891,7 +892,7 @@ namespace snmalloc
           return ticker.check_tick(r);
         },
         [](Allocator* a, size_t size) SNMALLOC_FAST_PATH_LAMBDA {
-          return a->small_alloc<Conts, CheckInitNoOp>(size);
+          return a->template small_alloc<Conts, CheckInitNoOp>(size);
         },
         size);
     }

src/test/snmalloc_testlib.cc

@@ -174,6 +174,12 @@ namespace snmalloc
   {
     Aal::pause();
   }
+
+  // Force-emit message_impl's COMDAT here so testlib-only tests (redblack,
+  // seqset) that see only its non-inline declaration can link. volatile keeps
+  // the odr-use non-elidable.
+  [[maybe_unused]] static void (*volatile force_message_impl)(
+    const char* const) = &message_impl;
 } // namespace snmalloc
 
 // -- override/malloc.cc symbols with testlib_ prefix -----------------------