[libc++] In tests, use `abort` to terminate upon an error.

[Mordante]

@ldionne asked the same here https://reviews.llvm.org/D142808#inline-1381137. This may lead to merge conflicts. So if this patch is not urgent I have a slight preference to abandon it.

Otherwise LGTM!

[ldionne]

This actually fixes some issues for us internally, so I'd like to ship it soon and even cherry-pick on release/16.x. The rebase should be realllly easy.

[Mordante]

In D143245#4119166, @ldionne wrote:

This actually fixes some issues for us internally, so I'd like to ship it soon and even cherry-pick on release/16.x. The rebase should be realllly easy.

Of course the rebase in easy, but I would like to prevent it if possible ;-)
Fixing issues for Apple internally sounds like a good reason to ship it and cherry-pick it for LLVM 16.

libcxx/test/support/assert_macros.h

 
 // Logs the error and calls exit.
 //
 // It shows a generic assert like message including a custom message. This
 // message should end with a newline.
 [[noreturn]] void test_log_error(const char* condition, const char* file, int line, std::string&& message) {
   const char* msg = condition ? "Assertion failure: " : "Unconditional failure:";
   std::fprintf(stderr, "%s%s %s %d\n%s", msg, condition, file, line, message.c_str());
-  exit(EXIT_FAILURE);
+  std::abort();
 }
 
 inline void test_fail(const char* file, int line, std::string&& message) {
   test_log_error("", file, line, std::move(message));
 }
 
 inline void test_require(bool condition, const char* condition_str, const char* file, int line, std::string&& message) {
   if (condition)