[flang-rt] Fix aarch64-libcxx build failure

There seems to be multiple declarations of __libcpp_verbose_abort, some
with noexcept and some without. Reverting to the previous
forward-declaration (without noexcept) which seemes to have worked
before.

Author: Meinersbur

flang-rt/lib/runtime/io-api-minimal.cpp

@@ -150,7 +150,7 @@ bool IODEF(OutputLogical)(Cookie cookie, bool truth) {
 // Provide own definition for `std::__libcpp_verbose_abort` to avoid dependency
 // on the version provided by libc++.
 
-void std::__libcpp_verbose_abort(char const *format, ...) noexcept {
+void std::__libcpp_verbose_abort(char const *format, ...) {
   va_list list;
   va_start(list, format);
   std::vfprintf(stderr, format, list);