makefile: update CPPFLAGS & CFLAGS

[clan]

1. _FORTIFY_SOURCE is defined built-in by compiler, so undefine the define to slience warnings like:

: warning: "_FORTIFY_SOURCE" redefined
: note: this is the location of the previous definition

2. -Wno-unknown-warning-option & -Wno-gnu-alignof-expression are available for clang only, but "-fplan9-extensions" is used which is gcc only! So remove these two warning options to avoid:

cc1: note: unrecognized command-line option ‘-Wno-gnu-alignof-expression’ may have been intended to silence earlier diagnostics
cc1: note: unrecognized command-line option ‘-Wno-unknown-warning-option’ may have been intended to silence earlier diagnostics

[lahwaacz]

Where do you get warning: "_FORTIFY_SOURCE" redefined ? The documentation for GCC at least says nothing about the need to undefine it: https://www.gnu.org/software/libc/manual/html_node/Source-Fortification.html

[clan]

Where do you get warning: "_FORTIFY_SOURCE" redefined ? The documentation for GCC at least says nothing about the need to undefine it: https://www.gnu.org/software/libc/manual/html_node/Source-Fortification.html

see: SELinuxProject/selinux@4f96b32
and discussion here: https://patchwork.kernel.org/project/selinux/patch/1544736761-7920-1-git-send-email-william.c.roberts@intel.com/

I encoutered this warning when compilng in Gentoo Hardened profile.