Remove _FORTIFY_SOURCE

Apparently, on some glibc versions this causes warnings when
optimization is not enabled.

Altogether, there appear to be too many incompatibilities surrounding
this.

src/template/linux

@@ -3,12 +3,6 @@
 # Force _GNU_SOURCE on; plperl is broken with Perl 5.8.0 otherwise
 CPPFLAGS="$CPPFLAGS -D_GNU_SOURCE"
 
-# Many distributors use this, so we might as well see the warnings as
-# well.  ICC doesn't work when this is enabled.
-if test "$ICC" != "yes"; then
-  CPPFLAGS="$CPPFLAGS -D_FORTIFY_SOURCE=2"
-fi
-
 # If --enable-profiling is specified, we need -DLINUX_PROFILE
 PLATFORM_PROFILE_FLAGS="-DLINUX_PROFILE"