Restore broken win32 build, include apr/std headers before httpd headers

Restore broken win32 build, include apr/std headers before httpd headers

 - In httpd we override exit() to trap the true exit code (see os/win32/os.h)
 - process.h was redefining exit() which picked up the macro instead of the
   original exit() declaration
 - Cleaner style pulls in apr, then standard C headers, and finally sets down
   the httpd includes on top of these, resolving the windows build regression

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1881477 13f79535-47bb-0310-9956-ffa450edef68