mesa: add support for CET to x86/x86-64 asm files.

Control-flow enforcement technology is a new instructions on x86
processors to denote where indirect jumps can land. Gcc auto adds
the instruction (which encodes as a NOP on older CPUs) to entrypoints
but assembler files need manual adding. This adds it to all the
entry points in the mesa x86/x86-64 assembler files.

This will only happen if mesa is built with the -fcf-protection flag
to gcc as some distros are wanting to do.

Acked-by: Eric Anholt <eric@anholt.net>

meson.build

@@ -1034,7 +1034,7 @@ elif cc.has_header_symbol('sys/mkdev.h', 'major')
   pre_args += '-DMAJOR_IN_MKDEV'
 endif
 
-foreach h : ['xlocale.h', 'sys/sysctl.h', 'linux/futex.h', 'endian.h', 'dlfcn.h', 'execinfo.h', 'sys/shm.h']
+foreach h : ['xlocale.h', 'sys/sysctl.h', 'linux/futex.h', 'endian.h', 'dlfcn.h', 'execinfo.h', 'sys/shm.h', 'cet.h']
   if cc.compiles('#include <@0@>'.format(h), name : '@0@'.format(h))
     pre_args += '-DHAVE_@0@'.format(h.to_upper().underscorify())
   endif