ec866e635e
("Windows 10 SDK build fixes") introduced CPP macros
timezone -> _timezone
tzname -> _tzname
but these names are common and the macros rewrite too much.
The name mapping is only required when building strftime.c
with Visual Studio 2017 and later. Move the definitions
into strftime.c.
Change-Id: Ic813bff842124595fd3d86761cee6dcea4ae44e4