[nsan] More unit tests for `float128`. (#165248)

Now that llvm-libc has `nextafterf128`.

compiler-rt/lib/nsan/tests/NSanUnitTest.cpp

diff --git a/compiler-rt/lib/nsan/tests/NSanUnitTest.cpp b/compiler-rt/lib/nsan/tests/NSanUnitTest.cpp
index d121292..73b5967 100644
--- a/compiler-rt/lib/nsan/tests/NSanUnitTest.cpp
+++ b/compiler-rt/lib/nsan/tests/NSanUnitTest.cpp
@@ -43,8 +43,8 @@
   ASSERT_EQ(GetULPDiff<FT>(-X, -Y), 3);
 
   // Values with larger differences.
-  static constexpr const __sanitizer::u64 MantissaSize =
-      __sanitizer::u64{1} << FTInfo<FT>::kMantissaBits;
+  static constexpr const __uint128_t MantissaSize =
+      __uint128_t{1} << FTInfo<FT>::kMantissaBits;
   ASSERT_EQ(GetULPDiff<FT>(1.0, next(2.0, 1.0)), MantissaSize - 1);
   ASSERT_EQ(GetULPDiff<FT>(1.0, 2.0), MantissaSize);
   ASSERT_EQ(GetULPDiff<FT>(1.0, next(2.0, 3.0)), MantissaSize + 1);
@@ -57,11 +57,6 @@
   TestFT<double, static_cast<double (*)(double, double)>(nextafter)>();
 }
 
-TEST(NSanTest, Float128) {
-  // Very basic tests. FIXME: improve when we have nextafter<__float128>.
-  ASSERT_EQ(GetULPDiff<__float128>(0.0, 0.0), 0);
-  ASSERT_EQ(GetULPDiff<__float128>(-0.0, 0.0), 0);
-  ASSERT_NE(GetULPDiff<__float128>(-0.01, 0.01), kMaxULPDiff);
-}
+TEST(NSanTest, Float128) { TestFT<__float128, nextafterf128>(); }
 
 } // end namespace __nsan