Is there a builtin alternative to std::put_time for GCC <5?

There are no functions other than put_time for the outputing of time provided in the chrono or the iomanip library.

The ctime library does provide: strftime, ctime, and asctime.

Since http://stackoverflow.com does not permit questions about finding 3^rd party libraries, I'm going to guess that you're just asking for someone to direct you on the use of strftime? std::put_time(c_time, "[%T%z %F] ") could be written in the format:

char foo[24];

if(0 < strftime(foo, sizeof(foo), "[%T%z %F] ", c_time)) cout << foo << endl;

Also, this is C++, not C, so I'd like to steer clear of C functions whenever possible.

That's a pretty silly mindset. put_time uses std::strftime underneath the hood.

ext.manip#10

Returns: An object of unspecified type ... where the function f is defined as:

template <class charT, class traits>
void f(basic_ios<charT, traits>& str, const struct tm* tmb, const charT* fmt) {
  /* ... */
  typedef time_put<charT, Iter> TimePut;

  /* ... */
}

And time_put's definition is in locale.time.put.virtuals#1:

Effects: Formats the contents of the parameter t into characters placed on the output sequence s. Formatting is controlled by the parameters format and modifier, interpreted identically as the format specifiers in the string argument to the standard library function strftime() ...