[Bug libstdc++/79017] Old PowerMac G5, MacPorts GCC 5.4, C++11 and "std::log2 has not been declared"

[noloader at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79017

--- Comment #1 from Jeffrey Walton <noloader at gmail dot com> ---
Also see Issue 53226 in the MacPorts issue tracker. "gcc5 @5.4: error:
'std::log2' has not been declared", https://trac.macports.org/ticket/53226.