features.h: fix build when BSD headers are not in include path

In our C library we try to provide a "clean" POSIX/ISO-C set of include
files that strictly conforming applications can use. However, we also
want to provide some extensions that are commonly available in BSD or
GNU systems.

These are normally provided in a separate directory
(headers/compatibility/bsd) and additionally guarded by compiler defines
that can either be explicitly set, or enabled by default if the language
standard (selected from the compiler command line) is one with GNU
extensions (this is the default for GCC). This is controlled by a header
file called features.h.

However, for some headers it is not so simple to split the GNU
extensions apart from the other parts of the file, because it's not just
extra functions, but additional flags and defines.

So, we need the "features.h" mechanism to be available even in the base
set of headers, but not enable anything if the BSD headers are not in
the search path. The simplest way to achieve this is to have an empty
features.h in the base set of headers, that can then be overriden by the
one in headers/compatibility/bsd if needed.

Fixes #18732

Change-Id: Ia54d1206c2fba378ae276ed4232aee8443180afb
Reviewed-on: https://review.haiku-os.org/c/haiku/+/7287
Reviewed-by: waddlesplash <waddlesplash@gmail.com>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>

More work towards hybrid support

* All packaging architecture dependent variables do now have a
respective suffix and are set up for each configured packaging
architecture, save for the kernel and boot loader variables, which
are still only set up for the primary architecture.
For convenience TARGET_PACKAGING_ARCH, TARGET_ARCH, TARGET_LIBSUPC++,
and TARGET_LIBSTDC++ are set to the respective values for the primary
packaging architecture by default.
* Introduce a set of MultiArch* rules to help with building targets for
multiple packaging architectures. Generally the respective targets are
(additionally) gristed with the packaging architecture. For libraries
the additional grist is usually omitted for the primary architecture
(e.g. libroot.so and <x86>libroot.so for x86_gcc2/x86 hybrid), so that
Jamfiles for targets built only for the primary architecture don't
need to be changed.
* Add multi-arch build support for all targets needed for the stage 1
cross devel package as well as for libbe (untested).

To be validated as part of bug #6386. Update glibc regex to 2.11, headers/posix/regex.h included. This imposes some changes in some of our sources using the regex.h,
mostly bin tools and mail kit. The use of __USE_GNU macro is needed for instance when the expected regex implementation is the GNU one.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@38031 a95241bf-73f2-0310-859d-f6bbb57e9c96

enabled legacy re_comp re_exec
this fixes bug 563


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@17337 a95241bf-73f2-0310-859d-f6bbb57e9c96

* libroot and the runtime loader are no longer built with kernel rules.
* New rule Ld, analogously to KernelLd.
* Added StaticLibrary parameter for supplying additional objects.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@15191 a95241bf-73f2-0310-859d-f6bbb57e9c96

Merged changes from branch build_system_redesign at revision 14573.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@14574 a95241bf-73f2-0310-859d-f6bbb57e9c96

This should fix the build after all the kernel/system renaming.
If anything is still broken (and was not before :)), please shout.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@12361 a95241bf-73f2-0310-859d-f6bbb57e9c96

Renamed src/kernel to src/system.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@12359 a95241bf-73f2-0310-859d-f6bbb57e9c96

More work towards hybrid support

* All packaging architecture dependent variables do now have a
respective suffix and are set up for each configured packaging
architecture, save for the kernel and boot loader variables, which
are still only set up for the primary architecture.
For convenience TARGET_PACKAGING_ARCH, TARGET_ARCH, TARGET_LIBSUPC++,
and TARGET_LIBSTDC++ are set to the respective values for the primary
packaging architecture by default.
* Introduce a set of MultiArch* rules to help with building targets for
multiple packaging architectures. Generally the respective targets are
(additionally) gristed with the packaging architecture. For libraries
the additional grist is usually omitted for the primary architecture
(e.g. libroot.so and <x86>libroot.so for x86_gcc2/x86 hybrid), so that
Jamfiles for targets built only for the primary architecture don't
need to be changed.
* Add multi-arch build support for all targets needed for the stage 1
cross devel package as well as for libbe (untested).

To be validated as part of bug #6386. Update glibc regex to 2.11, headers/posix/regex.h included. This imposes some changes in some of our sources using the regex.h,
mostly bin tools and mail kit. The use of __USE_GNU macro is needed for instance when the expected regex implementation is the GNU one.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@38031 a95241bf-73f2-0310-859d-f6bbb57e9c96

enabled legacy re_comp re_exec
this fixes bug 563


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@17337 a95241bf-73f2-0310-859d-f6bbb57e9c96

* libroot and the runtime loader are no longer built with kernel rules.
* New rule Ld, analogously to KernelLd.
* Added StaticLibrary parameter for supplying additional objects.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@15191 a95241bf-73f2-0310-859d-f6bbb57e9c96

Merged changes from branch build_system_redesign at revision 14573.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@14574 a95241bf-73f2-0310-859d-f6bbb57e9c96

This should fix the build after all the kernel/system renaming.
If anything is still broken (and was not before :)), please shout.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@12361 a95241bf-73f2-0310-859d-f6bbb57e9c96

Renamed src/kernel to src/system.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@12359 a95241bf-73f2-0310-859d-f6bbb57e9c96