[libc++][NFC] Fix copy-paste errors in tests

The test precision_type.pass.cpp was a duplicate of precision.pass.cpp,
so it is removed. atomic_flag_test.pass.cpp was a duplicate of
atomic_flag_test_and_set.pass.cpp, so instead I wrote a proper
test for it. Those duplicate tests were detected with

     find libcxx ! -empty -type f -exec md5sum {} + | sort | uniq -w32 -dD

libcxx/test/std/atomics/atomics.flag/atomic_flag_test.pass.cpp

@@ -12,8 +12,8 @@
 
 // struct atomic_flag
 
-// bool atomic_flag_test_and_set(volatile atomic_flag*);
+// bool atomic_flag_test(const volatile atomic_flag*);
-// bool atomic_flag_test_and_set(atomic_flag*);
+// bool atomic_flag_test(const atomic_flag*);
 
 #include <atomic>
 #include <cassert>
@@ -25,15 +25,17 @@ int main(int, char**)
     {
         std::atomic_flag f;
         f.clear();
-        assert(atomic_flag_test_and_set(&f) == 0);
+        assert(atomic_flag_test(&f) == 0);
-        assert(f.test_and_set() == 1);
+        assert(f.test_and_set() == 0);
+        assert(atomic_flag_test(&f) == 1);
     }
     {
         volatile std::atomic_flag f;
         f.clear();
-        assert(atomic_flag_test_and_set(&f) == 0);
+        assert(atomic_flag_test(&f) == 0);
-        assert(f.test_and_set() == 1);
+        assert(f.test_and_set() == 0);
+        assert(atomic_flag_test(&f) == 1);
     }
 
-  return 0;
+    return 0;
 }

libcxx/test/std/atomics/atomics.flag/atomic_flag_test_explicit.pass.cpp

@@ -111,5 +111,5 @@ int main(int, char**)
         assert(atomic_flag_test_explicit(&f, std::memory_order_seq_cst) == 1);
     }
 
-  return 0;
+    return 0;
 }

libcxx/test/std/utilities/time/time.hms/time.hms.members/precision.pass.cpp

@@ -44,7 +44,7 @@ constexpr unsigned long long powers[] = {
 	100000000000000000ULL,
 	1000000000000000000ULL,
 	10000000000000000000ULL
-	};
+};
 
 template <typename Duration, unsigned width>
 constexpr bool check_precision()

libcxx/test/std/utilities/time/time.hms/time.hms.members/precision_type.pass.cpp

@@ -1,80 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-// 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
-//
-//===----------------------------------------------------------------------===//
-// UNSUPPORTED: c++03, c++11, c++14, c++17
-// <chrono>
-
-// template <class Duration>
-// class hh_mm_ss
-// {
-// public:
-//     static unsigned constexpr fractional_width = see below;
-//     using precision                            = see below;
-//
-//   precision is duration<common_type_t<Duration::rep, seconds::rep>,
-//                                 ratio<1, 10^^fractional_width>>
-
-#include <chrono>
-#include <cassert>
-
-#include "test_macros.h"
-
-constexpr unsigned long long powers[] = {
-	1ULL,
-	10ULL,
-	100ULL,
-	1000ULL,
-	10000ULL,
-	100000ULL,
-	1000000ULL,
-	10000000ULL,
-	100000000ULL,
-	1000000000ULL,
-	10000000000ULL,
-	100000000000ULL,
-	1000000000000ULL,
-	10000000000000ULL,
-	100000000000000ULL,
-	1000000000000000ULL,
-	10000000000000000ULL,
-	100000000000000000ULL,
-	1000000000000000000ULL,
-	10000000000000000000ULL
-	};
-
-template <typename Duration, unsigned width>
-constexpr bool check_precision()
-{
-	using HMS = std::chrono::hh_mm_ss<Duration>;
-	using CT  = std::common_type_t<typename Duration::rep, std::chrono::seconds::rep>;
-	using Pre = std::chrono::duration<CT, std::ratio<1, powers[width]>>;
-	return std::is_same_v<typename HMS::precision, Pre>;
-}
-
-int main(int, char**)
-{
-	using microfortnights = std::chrono::duration<int, std::ratio<756, 625>>;
-
-	static_assert( check_precision<std::chrono::hours,                               0>(), "");
-	static_assert( check_precision<std::chrono::minutes,                             0>(), "");
-	static_assert( check_precision<std::chrono::seconds,                             0>(), "");
-	static_assert( check_precision<std::chrono::milliseconds,                        3>(), "");
-	static_assert( check_precision<std::chrono::microseconds,                        6>(), "");
-	static_assert( check_precision<std::chrono::nanoseconds,                         9>(), "");
-	static_assert( check_precision<std::chrono::duration<int, std::ratio<  1,   2>>, 1>(), "");
-	static_assert( check_precision<std::chrono::duration<int, std::ratio<  1,   3>>, 6>(), "");
-	static_assert( check_precision<std::chrono::duration<int, std::ratio<  1,   4>>, 2>(), "");
-	static_assert( check_precision<std::chrono::duration<int, std::ratio<  1,   5>>, 1>(), "");
-	static_assert( check_precision<std::chrono::duration<int, std::ratio<  1,   6>>, 6>(), "");
-	static_assert( check_precision<std::chrono::duration<int, std::ratio<  1,   7>>, 6>(), "");
-	static_assert( check_precision<std::chrono::duration<int, std::ratio<  1,   8>>, 3>(), "");
-	static_assert( check_precision<std::chrono::duration<int, std::ratio<  1,   9>>, 6>(), "");
-	static_assert( check_precision<std::chrono::duration<int, std::ratio<  1,  10>>, 1>(), "");
-	static_assert( check_precision<microfortnights,                                  4>(), "");
-
-	return 0;
-}