[libc] Reset rounding mode after fsetround tests

libc/test/src/fenv/rounding_mode_test.cpp

 //===-- Unittests for fegetround and fesetround ---------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "src/fenv/fegetround.h"
 #include "src/fenv/fesetround.h"
 
 #include "utils/UnitTest/Test.h"
 
 #include <fenv.h>
 
 TEST(LlvmLibcRoundingModeTest, SetAndGet) {
+  struct ResetDefaultRoundingMode {
+    int original;
+    ~ResetDefaultRoundingMode() {
+      __llvm_libc::fesetround(original);
+    }
+  } reset{__llvm_libc::fegetround()};
+
   int s = __llvm_libc::fesetround(FE_TONEAREST);
   EXPECT_EQ(s, 0);
   int rm = __llvm_libc::fegetround();
   EXPECT_EQ(rm, FE_TONEAREST);
 
   s = __llvm_libc::fesetround(FE_UPWARD);
   EXPECT_EQ(s, 0);
   rm = __llvm_libc::fegetround();