to be aligned with seastar's coding-style.md: scylladb uses seastar's
coding-style.md. so let's adhere to it.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closes#15345
Recently, clang started complaining about std::unexpected_handler being
deprecated:
```
In file included from utils/exceptions.cc:18:
./utils/abi/eh_ia64.hh:26:10: warning: 'unexpected_handler' is deprecated [-Wdeprecated-declarations]
std::unexpected_handler unexpectedHandler;
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/12/../../../../include/c++/12/exception:84:18: note: 'unexpected_handler' has been explicitly marked deprecated here
typedef void (*_GLIBCXX11_DEPRECATED unexpected_handler) ();
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/12/../../../../include/c++/12/x86_64-redhat-linux/bits/c++config.h:2343:32: note: expanded from macro '_GLIBCXX11_DEPRECATED'
^
/usr/bin/../lib/gcc/x86_64-redhat-linux/12/../../../../include/c++/12/x86_64-redhat-linux/bits/c++config.h:2334:46: note: expanded from macro '_GLIBCXX_DEPRECATED'
^
1 warning generated.
```
According to cppreference.com, it was deprecated in C++11 and removed in
C++17 (!).
This commit gets rid of the warning by inlining the
std::unexpected_handler typedef, which is defined as a pointer a
function with 0 arguments, returning void.
Fixes: #12022Closes#12074
Adds a header for utility functions/structures, based on the Itanium ABI
for C++, necessary for us to inspect exceptions behind
std::exception_ptr without having to actually rethrow the exception.
