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.
OK for trunk? Igor