Comment 1 for bug 1169164

Looking at differences between x86_64 and aarch64 versions of signal.h, both include sys/ucontext.h, where only the aarch64 version includes <sys/procfs.h> which in turn says:

/* Anyway, the whole purpose of this file is for GDB and GDB only.
     Don't read too much into it. Don't use it for anything other than
     GDB unless you know what you are doing. */

Doesn't seem like including it from a posix header like <signal.h> is safe.