The recent patch to remove poly_int_pod triggers a bug in g++ 4.8.5's
C++ 11 support which mistakenly believes poly_uint16 has a non-trivial
constructor.  This in turn prohibits it from being used as a member in
a union (rtxunion) that constructed statically, resulting in a (fatal)
error during stage 1.  A workaround is to add an explicit constructor
to the problematic union, which allows mainline to be bootstrapped with
the system compiler on older RedHat 7 systems.

This patch has been tested on x86_64-pc-linux-gnu where it allows a
bootstrap to complete when using g++ 4.8.5 as the host compiler.
Ok for mainline?


2023-10-04  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	* rtl.h (rtx_def::u): Add explicit constructor to workaround
	issue using g++ 4.8 as a host compiler.