x86: Add ENDBR at function entries
Intel Control-flow Enforcement Technology (CET):
https://software.intel.com/en-us/articles/intel-sdm
contains shadow stack (SHSTK) and indirect branch tracking (IBT). When CET is enabled, ELF object files must be marked with .note.gnu.property section. Also when IBT is enabled, all indirect branch targets must start with ENDBR instruction which is NOP on non-CET processors.
This fixes: