Add/check support for older compilers

[jvoisin]

As reported on irc:

17:36 <f_> jvoisin: is fortify-headers expected to work on ancient gcc versions?
17:37 <f_> I get this error when building with gcc6: /usr/include/fortify/fortify-headers.h:56:67: error: missing binary operator before token "("
17:37 <f_>  #if _FORTIFY_SOURCE > 2 && defined __has_builtin && __has_builtin (__builtin_dynamic_object_size)
18:10 <f_> the usecase here is compiling kernels in postmarketOS, that are downstream vendor kernels (think 3.x, 4.x)
18:10 <f_> I caught this while upgrading a bunch of our device ports to armv7 from armhf
18:10 <f_> (because they target armv7 devices, and have no reason to be armhf)
18:11 <f_> jvoisin: pmOS repositories have gcc4 and gcc6 packages, if that helps
18:11 <f_> https://pkgs.postmarketos.org/packages?name=gcc4&branch=master&repo=&arch=&origin= https://pkgs.postmarketos.org/packages?name=gcc6&branch=master&repo=&arch=&origin=

[sertonix]

I suspect that splitting the usage of __has_builtin into a seperate #if would fix the issue

[JustSoup312]

With GCC 4.9.2 I am also getting variations of:

/usr/include/fortify/unistd.h:44:30: error: expected ')' before numeric constant
 __fortify_access(write_only, 2, 3)
                              ^
/usr/include/fortify/unistd.h:160:29: error: expected ')' before numeric constant
__fortify_access(read_only, 2, 3)
                             ^
/usr/include/fortify/string.h:113:30: error: expected ')' before numeric constant
 __fortify_access(read_write, 1)
                              ^
/usr/include/fortify/stdlib.h:42:26: error: expected ')' before '==' token
 __fortify_warning_if(__p == NULL, "'realpath' called with path set to `NULL`; did you invert the arguments?")
                          ^
/usr/include/fortify/stdio.h:40:30: error: expected ')' before numeric constant
 __fortify_access(read_write, 1, 2)
                              ^
/usr/include/fortify/stdio.h:79:27: error: expected ')' before numeric constant
 __fortify__format(printf, 3, 0)
                           ^
/usr/include/fortify/sys/socket.h:37:30: error: expected ')' before numeric constant
 __fortify_access(write_only, 2, 3)
                              ^
/usr/include/fortify/sys/socket.h:60:29: error: expected ')' before numeric constant
 __fortify_access(read_only, 2, 3)
                             ^

[sertonix]

I think that is already fixed on the master branch: fa01a69

[JustSoup312]

Oops you are totally right. For some reason my environment was using the release headers instead of the master ones, even though I had pointed to the master ones. Please ignore.