Tested with
make check RUNTESTFLAGS="conformance.exp=*numeric*synopsis* --target_board=unix/-std=$std"
for std in {c++98, c++11, c++17, c++2a}.
libstdc++-v3/ChangeLog:
* testsuite/26_numerics/headers/numeric/synopsis.cc: Add signatures for
functions introduced in C++11, C++17 and C++2a. Add 'constexpr' to
existing signatures for C++2a.
799270b430