Merge r1626050 from trunk:

Concat string at compile time when possible.
Doing so, sometimes also give the opportunity to turn a 'ap_fputstrs' into a 'ap_fputs'.
PR 53741
Submitted by: jailletc36
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1634525 13f79535-47bb-0310-9956-ffa450edef68