Fix workaround for google/benchmark with C++20

[coryan]

When we compile google/benchmark with C++20 on Fedora:36 we get a strange error (see below) from this line:

https://github.com/google/benchmark/blob/v1.6.2/src/benchmark.cc#L488

We are working around this by compiling just that library with C++17.

#17 13.16                  from /var/tmp/build/include/benchmark/benchmark.h:186,
#17 13.16                  from /var/tmp/build/src/benchmark.cc:15:
#17 13.16 In static member function 'static constexpr std::char_traits<char>::char_type* std::char_traits<char>::copy(char_type*, const char_type*, std::size_t)',
#17 13.16     inlined from 'static constexpr void std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::_S_copy(_CharT*, const _CharT*, size_type) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]' at /usr/include/c++/12/bits/basic_string.h:423:21,
#17 13.16     inlined from 'constexpr std::__cxx11::basic_string<_CharT, _Traits, _Allocator>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::_M_replace(size_type, size_type, const _CharT*, size_type) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]' at /usr/include/c++/12/bits/basic_string.tcc:532:22,
#17 13.16     inlined from 'constexpr std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::assign(const _CharT*) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]' at /usr/include/c++/12/bits/basic_string.h:1647:19,
#17 13.16     inlined from 'constexpr std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator=(const _CharT*) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]' at /usr/include/c++/12/bits/basic_string.h:815:28,
#17 13.16     inlined from 'size_t benchmark::RunSpecifiedBenchmarks(BenchmarkReporter*, BenchmarkReporter*, std::string)' at /var/tmp/build/src/benchmark.cc:488:12:
#17 13.16 /usr/include/c++/12/bits/char_traits.h:431:56: error: 'void* __builtin_memcpy(void*, const void*, long unsigned int)' accessing 9223372036854775810 or more bytes at offsets [2, 9223372036854775807] and 1 may overlap up to 9223372036854775813 bytes at offset -3 [-Werror=restrict]
#17 13.16   431 |         return static_cast<char_type*>(__builtin_memcpy(__s1, __s2, __n));
#17 13.16       |                                        ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
#17 13.26 cc1plus: all warnings being treated as errors

[hitesh-kumain]

Can you please assign this to me?...

[coryan]

This has been diagnosed as a GCC / libstd++ bug, see:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105651 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105329

I figured this out by reading:

https://github.com/google/benchmark/issues/1398

I think the best thing to do in the google-cloud-cpp project is to wait for these fixes to make it to the Fedora version we use for our builds and then remove the workaround.

[coryan]

Still blocked, we need to get back in sync with the google/benchmark support matrix.