[libc++] Remove trailing newline from _LIBCPP_ASSERTION_HANDLER calls (#143573)

This newline was originally added in https://reviews.llvm.org/D142184
but I think updating `__libcpp_verbose_abort` to add newline instead is
more consistent, and works for other callers of `_LIBCPP_VERBOSE_ABORT`.

The `_LIBCPP_ASSERTION_HANDLER` calls through to either
`_LIBCPP_VERBOSE_ABORT` macro or the `__builtin_verbose_trap`. From what
I can tell neither of these function expect a trailing newline (at least
none of the usage of `_LIBCPP_VERBOSE_ABORT` or `__builtin_verbose_trap`
that I can find include a trailing newline except `_LIBCPP_ASSERTION_HANDLER`).

I noticed this discrepancy when working on
https://github.com/emscripten-core/emscripten/pull/24543

1 files changed, 3 insertions, 0 deletions

diff --git a/libcxx/src/verbose_abort.cpp b/libcxx/src/verbose_abort.cpp
index 94bdb45..efb7b9b 100644
--- a/libcxx/src/verbose_abort.cpp
+++ b/libcxx/src/verbose_abort.cpp
@@ -30,6 +30,9 @@ _LIBCPP_WEAK void __libcpp_verbose_abort(char const* format, ...) noexcept {
     va_list list;
     va_start(list, format);
     std::vfprintf(stderr, format, list);
+    // Callers of `__libcpp_verbose_abort` do not include a newline but when
+    // writing the message to stderr we need to include one.
+    std::fputc('\n', stderr);
     va_end(list);
   }