ENDBR32 and RDSSPD are multi-byte NOPs on x86-64 processors and
newer x86 processors, starting Pentium Pro.  They are UD on older
32-bit processors. Detect this at configure time and adjust the
default value for enable_cet. GCC will enable CET in 32-bit run-time
libraries in any case if --enable-cet is used to configure GCC.

	PR target/84148
	* config/cet.m4: Check if target support multi-byte NOPS (SSE).
	* libatomic/configure: Regenerate.
	* libbacktrace/configure: Likewise.
	* libgcc/configure: Likewise.
	* libgfortran/configure: Likewise.
	* libgomp/configure: Likewise.
	* libitm/configure: Likewise.
	* libmpx/configure: Likewise.
	* libobjc/configure: Likewise.
	* libquadmath/configure: Likewise.
	* libsanitizer/configure: Likewise.
	* libssp/configure: Likewise.
	* libstdc++-v3/configure: Likewise.
	* libvtv/configure: Likewise.

From-SVN: r257809