[memory linux] Properly unlink shared memory

shm_unlink(name) is the proper way to close a shared memory in linux.
Prior to this, xenia was creating and not cleaning up shared memory handle
which would accumulate in /dev/shm. shm_unlink is the proper way of doing
this.
Add filename to CloseFileMappingHandle signature.
Add simple test to open and close.

src/xenia/cpu/backend/x64/x64_code_cache.cc

@@ -43,7 +43,7 @@ X64CodeCache::~X64CodeCache() {
   if (mapping_) {
     xe::memory::UnmapFileView(mapping_, generated_code_base_,
                               kGeneratedCodeSize);
-    xe::memory::CloseFileMappingHandle(mapping_);
+    xe::memory::CloseFileMappingHandle(mapping_, file_name_);
     mapping_ = nullptr;
   }
 }