configure: Implement --enable-host-pie

configure: Implement --enable-host-pie

This patch implements the --enable-host-pie configure option which
makes the compiler executables PIE.  This can be used to enhance
protection against ROP attacks, and can be viewed as part of a wider
trend to harden binaries.

Co-Authored by: Iain Sandoe  <iain@sandoe.co.uk>

	* configure.ac (--enable-host-pie): New check.  Set PICFLAG after this
	check.

intl/
	* configure.ac (--enable-host-shared): Don't set PICFLAG here.
	(--enable-host-pie): New check.  Set PICFLAG after this check.

libdecnumber/
	* configure.ac (--enable-host-shared): Don't set PICFLAG here.
	(--enable-host-pie): New check.  Set PICFLAG after this check.

zlib/
	* configure.ac (--enable-host-shared): Don't set PICFLAG here.
	(--enable-host-pie): New check.  Set PICFLAG after this check.