Support the suppress-error-charset setting, as with Apache 1.3.x.

With Apache 1.3.x, it is a bit simpler as the request does
not go through ap_make_content_type().

Modules can set custom error responses but not be able to
set the charset, so they have to code the charset in the
html.  Thus, it is useful to preserve 1.3.x behavior exactly.

PR: 26467


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@170354 13f79535-47bb-0310-9956-ffa450edef68