Fix httpd's definition of LTFLAGS to be consistent with that of apr

and apr-util, allow it to be overridden by the configure command-line
(default="--silent") and introduce LT_LDFLAGS to replace what we were
formally abusing as LTFLAGS.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@89094 13f79535-47bb-0310-9956-ffa450edef68