[clang][Sema] Restore switch-default.cpp test case

This test case exists upstream currently. It was deleted by
mistake when reapplying the patch:
 [clang][Sema] Add -Wswitch-default warning option (llvm#73077)

The test case had been added upstream for a subsequent patch
 [Clang][Sema] Fix Wswitch-default bad warning in template (llvm#76007)

Change-Id: I94fdbe2daa4703166e0d7fc00a3a4d08f98ae410

clang/test/Sema/switch-default.cpp

@@ -0,0 +1,53 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 -Wswitch-default %s
+
+int f1(int a) {
+  switch (a) {                // expected-warning {{'switch' missing 'default' label}}
+    case 1: a++; break;
+    case 2: a += 2; break;
+  }
+  return a;
+}
+
+int f2(int a) {
+  switch (a) {                // no-warning
+    default:
+      ;
+  }
+  return a;
+}
+
+// Warn even completely covered Enum cases(GCC compatibility).
+enum E { A, B };
+enum E check_enum(enum E e) {
+  switch (e) {                // expected-warning {{'switch' missing 'default' label}}
+    case A: break;
+    case B: break;
+  }
+  return e;
+}
+
+template<typename Index>
+int t1(Index i)
+{
+  switch (i) {              // expected-warning {{'switch' missing 'default' label}}
+    case 0: return 0;
+    case 1: return 1;
+  }
+  return 0;
+}
+
+template<typename Index>
+int t2(Index i)
+{
+  switch (i) {            // no-warning
+    case 0: return 0;
+    case 1: return 1;
+    default: return 2;
+  }
+  return 0;
+}
+
+int main() {
+  return t1(1);       // expected-note {{in instantiation of function template specialization 't1<int>' requested here}}
+}
+