[libc++] Update and normalize the "all the headers" tests.

Some C++20 headers weren't added properly to all three of these
test files. Add them, and take the time to normalize the formatting
so that

    diff <(grep '#include' foo.cpp) <(grep '#include' bar.cpp)

shows no diffs (except that `no_assert_include` deliberately
excludes `<cassert>`).

- Add macro guards to <{barrier,latch,semaphore}>.
- Add macro guards to <experimental/simd>.
- Remove an include of <cassert> from <semaphore>.
- Instead, include <cassert> in the semaphore tests.

Differential Revision: https://reviews.llvm.org/D92525

GitOrigin-RevId: d430330788c646afcb2c32c8f24c63210b518a32
diff --git a/include/semaphore b/include/semaphore
index 8f63162..0943606 100644
--- a/include/semaphore
+++ b/include/semaphore
@@ -49,7 +49,6 @@
 #include <__availability>
 #include <__threading_support>
 #include <atomic>
-#include <cassert>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
@@ -59,6 +58,9 @@
 # error <semaphore> is not supported on this single threaded system
 #endif
 
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
 #if _LIBCPP_STD_VER >= 14
 
 _LIBCPP_BEGIN_NAMESPACE_STD
@@ -233,4 +235,6 @@
 
 #endif // _LIBCPP_STD_VER >= 14
 
+_LIBCPP_POP_MACROS
+
 #endif //_LIBCPP_SEMAPHORE