Tweak server/Makefile so that the rules for generating exports.c

are compatible with make utilities which don't expand wildcards
in a dependency list (e.g., OS/390 make, certain levels of GNU
make).


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@90167 13f79535-47bb-0310-9956-ffa450edef68