fortify-headers adds a UD2 instruction because the compiler cannot
determine the size of "spjump_start" that is used with memmove
in the remap_spjump() function of pmcl-kernel.c. Disabling this
allows CCL to run without encountering an "Illegal instruction".

--- a/lisp-kernel/linuxx8664/Makefile
+++ b/lisp-kernel/linuxx8664/Makefile
@@ -23,7 +23,7 @@
 M4FLAGS = -DLINUX -DX86 -DX8664 -DHAVE_TLS
 CDEFINES = -DLINUX -D_REENTRANT -DX86 -DX8664 -D_GNU_SOURCE -DHAVE_TLS  -DVC_REVISION=$(VC_REVISION) #-DDISABLE_EGC -DUSE_FUTEX
 CDEBUG = -g
-COPT = -O2
+COPT = -O2 -U_FORTIFY_SOURCE
 # Once in a while, -Wformat says something useful.  The odds are against that,
 # however.
 WFORMAT = -Wno-format