While compiling under Emscripten with _LP64 being 0, Clang complains
that the format specifier does not match the actual type (even though
size_t and unsigned are probably compatible.)
As per https://gitlab.kitware.com/cmake/cmake/-/issues/18121,
check_library_exists cannot not determine the availability of a symbol
in a static library. Switch to check_cxx_symbol_exists to avoid
incorrectly detecting the presence of dbghelp.
The preprocessor defines interfere with method declarations, e.g., in
std::basic_filebuf, resulting in following error:
C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.37.32822\include\fstream(376,26): error C2039: '_close': is not a member of 'std::basic_filebuf<char,std::char_traits<char>>' [D:\a\glog\glog\build_Debug\logging_unittest.vcxproj]
C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.37.32822\include\iosfwd(244,35): message : see declaration of 'std::basic_filebuf<char,std::char_traits<char>>' [D:\a\glog\glog\build_Debug\logging_unittest.vcxproj]
C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.37.32822\include\fstream(375,10): message : while compiling class template member function 'void std::basic_ofstream<char,std::char_traits<char>>::_close(void)' [D:\a\glog\glog\build_Debug\logging_unittest.vcxproj]
D:\a\glog\glog\src\logging_unittest.cc(788,12): message : see the first reference to 'std::basic_ofstream<char,std::char_traits<char>>::_close' in 'TestBasenameAppendWhenNoTimestamp' [D:\a\glog\glog\build_Debug\logging_unittest.vcxproj]
D:\a\glog\glog\src\logging_unittest.cc(786,12): message : see reference to class template instantiation 'std::basic_ofstream<char,std::char_traits<char>>' being compiled [D:\a\glog\glog\build_Debug\logging_unittest.vcxproj]
glog is used on a variety of systems, and we must assume that some of
them still use vulnerable mailers that have bugs or "interesting
features" such as https://nvd.nist.gov/vuln/detail/CVE-2004-2771.
Let's protect users against accidental shell injection by validating
the email addresses against a slightly stricter version of the regex
used by HTML5 to validate addresses[1].
This should prevent triggering any unexpected behavior in these tools.
Also add some basic unit tests for the SendEmail method.
[1] https://html.spec.whatwg.org/multipage/input.html#valid-e-mail-address
