* configure.in: Add --enable-pie flag; define PICFLAGS and PILDFLAGS.

* build/rules.mk.in: Factor out BASE_CC and BASE_CXX from COMPILE.
Substitute PICFLAGS into COMPILE and CXX_COMPILE, but not into
{SH,LT}{,_CXX}_COMPILE.  Substitute PILDFLAGS into LINK but not
{SH,MOD}_LINK.

Reviewed by: jerenkrantz


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@126362 13f79535-47bb-0310-9956-ffa450edef68