Fix strptime era handling, add more era tests [BZ #24394]

[Joseph Myers]

On Thu, 28 Mar 2019, Carlos O'Donell wrote:

> (a) Explicit code points.
> 
> I would like to see something like this:
> 
> "<U5E73><U6210>3<U5E74>"
> 
> Which is then converted by the test framework into the output encoding.

Using \u escape sequences in the string would be better (provided you want 
a UTF-8 string, -fexec-charset=utf-8 is the GCC default and is implemented 
entirely within GCC without depending on what iconv support might be 
available for the host GCC runs on).  Note that we already have various 
tests using \u.

(For tests using non-UTF-8 encodings, hex escape sequences for the 
individual characters may be safer, to avoid dependence on iconv support 
linked into GCC.)

-- 
Joseph S. Myers
joseph@codesourcery.com