-D_XOPEN_SOURCE=700 breaks build with non-glibc

[jbeich]

On BSDs libc exposes all features by default. When _XOPEN_SOURCE is specified non-standard features are hidden. Cheating compliance is possible but _DEFAULT_SOURCE (GNU) has no effect because the knob name is different: __BSD_VISIBLE on DragonFly/FreeBSD/OpenBSD and _NETBSD_SOURCE on NetBSD.

Also, usleep was removed in POSIX.1-2008 (-D_XOPEN_SOURCE=700).

$ cc --version
FreeBSD clang version 14.0.5 (https://github.com/llvm/llvm-project.git llvmorg-14.0.5-0-gc12386ae247c)
Target: x86_64-unknown-freebsd14.0
Thread model: posix
InstalledDir: /usr/bin

$ gmake
[...]
src/config.c:483:22: error: use of undeclared identifier 'DT_DIR'
                if (ent->d_type == DT_DIR)
                                   ^
src/ipc.c:53:6: warning: implicit declaration of function 'flock' is invalid in C99 [-Wimplicit-function-declaration]
        if (flock(lfd, LOCK_EX | LOCK_NB))
            ^
src/ipc.c:53:17: error: use of undeclared identifier 'LOCK_EX'
        if (flock(lfd, LOCK_EX | LOCK_NB))
                       ^
src/ipc.c:53:27: error: use of undeclared identifier 'LOCK_NB'
        if (flock(lfd, LOCK_EX | LOCK_NB))
                                 ^
src/keyboard.c:224:4: warning: implicit declaration of function 'usleep' is invalid in C99 [-Wimplicit-function-declaration]
                        usleep(ent->data*1E3);
                        ^
src/vkbd/uinput.c:262:3: warning: implicit declaration of function 'usleep' is invalid in C99 [-Wimplicit-function-declaration]
                usleep(100000);
                ^
src/vkbd/uinput.c:298:3: warning: implicit declaration of function 'usleep' is invalid in C99 [-Wimplicit-function-declaration]
                usleep(100000);
                ^
src/vkbd/uinput.c:332:3: warning: implicit declaration of function 'usleep' is invalid in C99 [-Wimplicit-function-declaration]
                usleep(100000);
                ^

[rvaiya]

Thanks. Keeping the feature test macros straight can be a chore :P. I'm not sure why I originally included both _XOPEN_SOURCE and _DEFAULT_SOURCE, presumably the former preceded the letter and ended up as residual cruft.