[test][ASan][Win] Print more info when LoadLibrary fails

[aeubanks]

rename some vars

[hans]

lgtm

compiler-rt/test/asan/TestCases/Windows/dll_host.cpp

72

I assume we're going to exit soon after this anyway, but it still seems nice to LocalFree(buf)

compiler-rt/test/asan/TestCases/Windows/dll_host.cpp

if (argc != 2) {
     printf("Usage: %s [client].dll\n", argv[0]);
     return 101;
   }
 
   const char *dll_name = argv[1];
 
   HMODULE h = LoadLibrary(dll_name);
   if (!h) {
-    printf("Could not load DLL: %s (code: %lu)!\n",
-           dll_name, GetLastError());
+    DWORD err = GetLastError();
+    printf("Could not load DLL: %s (code: %lu)!\n", dll_name, err);
+
+    LPSTR buf;
+
+    FormatMessageA(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM |
+                       FORMAT_MESSAGE_IGNORE_INSERTS,
+                   NULL, err, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), buf, 0,
+                   NULL);
+
+    printf("Error: %s\n", buf);
+
+    LocalFree(buf);
+
     return 102;
   }
 
   typedef int (*test_function)();
   test_function gf = (test_function)GetProcAddress(h, "test_function");
   if (!gf) {
     printf("Could not locate test_function in the DLL!\n");
     FreeLibrary(h);
     return 103;
   }
 
   int ret = gf();
 
   FreeLibrary(h);
   return ret;
 }