Add capability to OS abstract on Unix systems, with either functions,

inlines or macros. All code in os.c, os.h and os-inline.c is available
to all Apache source files. Only GCC is known to support inline at this
stage.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@79186 13f79535-47bb-0310-9956-ffa450edef68