[libc][nfc] Silence two warnings in tests

These currently give warnings for unused variables or a default case
where everything is covered.

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D153137

libc/test/UnitTest/RoundingModeUtils.cpp

@@ -20,19 +20,14 @@ int get_fe_rounding(RoundingMode mode) {
   switch (mode) {
   case RoundingMode::Upward:
     return FE_UPWARD;
-    break;
   case RoundingMode::Downward:
     return FE_DOWNWARD;
-    break;
   case RoundingMode::TowardZero:
     return FE_TOWARDZERO;
-    break;
   case RoundingMode::Nearest:
     return FE_TONEAREST;
-    break;
-  default:
-    __builtin_unreachable();
   }
+  __builtin_unreachable();
 }
 
 ForceRoundingMode::ForceRoundingMode(RoundingMode mode) {

libc/test/src/__support/uint_test.cpp

@@ -25,7 +25,6 @@ using LL_Int128 = __llvm_libc::cpp::Int<128>;
 using LL_Int192 = __llvm_libc::cpp::Int<192>;
 
 TEST(LlvmLibcUIntClassTest, BasicInit) {
-  LL_UInt128 empty;
   LL_UInt128 half_val(12345);
   LL_UInt128 full_val({12345, 67890});
   ASSERT_TRUE(half_val != full_val);