Use a more portable way to access the configuration.

Author: mjp41

src/snmalloc/override/malloc-extensions.cc

@@ -6,8 +6,8 @@ using namespace snmalloc;
 
 void get_malloc_info_v1(malloc_info_v1* stats)
 {
-  auto curr = StandardConfig::Backend::get_current_usage();
-  auto peak = StandardConfig::Backend::get_peak_usage();
+  auto curr = Alloc::Config::Backend::get_current_usage();
+  auto peak = Alloc::Config::Backend::get_peak_usage();
   stats->current_memory_usage = curr;
   stats->peak_memory_usage = peak;
 }