[Clang][NFC] Added testcase from #49549

The issue is fixed in trunk, so add testcase to avoid regression in the future.

Author: davidbolvansky

clang/test/SemaCXX/attr-likelihood.cpp

@@ -159,4 +159,18 @@ constexpr int constexpr_function() {
   [[likely]] return 0;
 }
 static_assert(constexpr_function() == 0);
+
+constexpr double pow(double x, long long n) noexcept {
+    if (n > 0) [[likely]]
+        return x * pow(x, n - 1);
+    else [[unlikely]]
+        return 1;
+}
+constexpr long long fact(long long n) noexcept {
+    if (n > 1) [[likely]]
+        return n * fact(n - 1);
+    else [[unlikely]]
+        return 1;
+}
+
 #endif