[libc] Enable hermetic floating point tests

[jhuber6]

Summary

This patch enables us to run the floating point tests as hermetic.
Importantly we now use the internal versions of the fesetround and
fegetround functions.

[michaelrj]

LGTM

libc/test/UnitTest/RoundingModeUtils.cpp

 //===-- RoundingModeUtils.cpp ---------------------------------------------===//
 //
 // 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 "RoundingModeUtils.h"
 
-#include <fenv.h>
+#include "src/__support/FPUtil/FEnvImpl.h"
 
 namespace __llvm_libc {
 namespace fputil {
 namespace testing {
 
 int get_fe_rounding(RoundingMode mode) {
   switch (mode) {
   case RoundingMode::Upward:
case RoundingMode::Nearest:
     return FE_TONEAREST;
     break;
   default:
     __builtin_unreachable();
   }
 }
 
 ForceRoundingMode::ForceRoundingMode(RoundingMode mode) {
-  old_rounding_mode = fegetround();
+  old_rounding_mode = get_round();
   rounding_mode = get_fe_rounding(mode);
   if (old_rounding_mode != rounding_mode)
-    fesetround(rounding_mode);
+    set_round(rounding_mode);
 }
 
 ForceRoundingMode::~ForceRoundingMode() {
   if (old_rounding_mode != rounding_mode)
-    fesetround(old_rounding_mode);
+    set_round(old_rounding_mode);
 }
 
 } // namespace testing
 } // namespace fputil
 } // namespace __llvm_libc

libc/test/src/CMakeLists.txt

 function(add_fp_unittest name)
   cmake_parse_arguments(
     "MATH_UNITTEST"
-    "NEED_MPFR;HERMETIC_TEST_ONLY" # Optional arguments
+    "NEED_MPFR;UNIT_TEST_ONLY;HERMETIC_TEST_ONLY" # Optional arguments
     "" # Single value arguments
     "LINK_LIBRARIES" # Multi-value arguments
     ${ARGN}
   )
 
   if(MATH_UNITTEST_NEED_MPFR)
     if(NOT LIBC_TESTS_CAN_USE_MPFR)
       message(VERBOSE "Math test ${name} will be skipped as MPFR library is not available.")
       return()
     endif()
   endif()
 
   if(MATH_UNITTEST_HERMETIC_TEST_ONLY)
     set(test_type HERMETIC_TEST_ONLY)
+  elseif(MATH_UNITTEST_UNIT_TEST_ONLY)
+    set(test_type UNIT_TEST_ONLY)
   endif()
   if(MATH_UNITTEST_NEED_MPFR)
     if(MATH_UNITTEST_HERMETIC_TEST_ONLY)
       message(FATAL "Hermetic math test cannot require MPFR.")
     endif()
     set(test_type UNIT_TEST_ONLY)
     list(APPEND MATH_UNITTEST_LINK_LIBRARIES libcMPFRWrapper libc_math_test_utils -lmpfr -lgmp)
   endif()
   list(APPEND MATH_UNITTEST_LINK_LIBRARIES LibcFPTestHelpers)
 
-  add_libc_unittest(
+  add_libc_test(
     ${name}
     ${test_type}
     LINK_LIBRARIES "${MATH_UNITTEST_LINK_LIBRARIES}"
     "${MATH_UNITTEST_UNPARSED_ARGUMENTS}"
   )
 endfunction(add_fp_unittest)
 
 add_subdirectory(__support)

libc/test/src/fenv/CMakeLists.txt

add_fp_unittest(
     DEPENDS
       libc.include.signal
       libc.src.fenv.feclearexcept
       libc.src.fenv.feraiseexcept
       libc.src.fenv.fetestexcept
       libc.src.__support.FPUtil.fenv_impl
     LINK_LIBRARIES
       LibcFPExceptionHelpers
+    UNIT_TEST_ONLY
   )
 
   add_fp_unittest(
     feholdexcept_test
     SUITE
       libc_fenv_unittests
     SRCS
       feholdexcept_test.cpp
     DEPENDS
       libc.include.fenv
       libc.src.fenv.feholdexcept
       libc.src.__support.FPUtil.fenv_impl
     LINK_LIBRARIES
       LibcFPExceptionHelpers
+    UNIT_TEST_ONLY
   )
 endif()