POSIX/GNU compliance macros fixes for uClibc support

[pcercuei]

Hi,

These two patches allow me to build wlroots with uClibc.

• _XOPEN_SOURCE is required for strdup to become available. Since it defines _POSIX_C_SOURCE (see man feature_test_macros(7)), remove all inline defines of these two macros, and have meson provide only the former.
• F_DUPFD_CLOEXEC seems to be a GNU-only thing, and will be provided by <fcntl.h> only when _GNU_SOURCE is defined on uClibc.

[emersion]

meson: define _XOPEN_SOURCE globally

Nack, we record what POSIX revision each source file needs, just like we record which header files it requires.

render/dmabuf: define _GNU_SOURCE for F_DUPFD_CLOEXEC

Nack, this is POSIX: https://pubs.opengroup.org/onlinepubs/9699919799/functions/fcntl.html

In general we only use POSIX functions, apart from where it's really not possible to do otherwise (e.g. session handling).

[pcercuei]

Well, it needs _XOPEN_SOURCE defined everywhere strdup() is used, and _GNU_SOURCE for F_DUPFD_CLOEXEC (even though these are POSIX) to compile on uClibc.

[emersion]

uClibc is wrong here. strdup is POSIX, and so is F_DUPFD_CLOEXEC, so only _POSIX_C_SOURCE should be required. Please report a uClibc bug.

[pcercuei]

uClibc is wrong here, but so is glibc. strdup() conforms to POSIX.1-2001 (according to its man page), so half of your code base could probably use _POSIX_C_SOURCE=200112L, but doesn't just so that it compiles with a broken library (glibc only exports strdup when _POSIX_C_SOURCE=200809L).

I'll try to send a patch to uClibc without too much hope (they probably have reasons why this has been broken for 20 years) but that won't change the fact that wlroots cannot be compiled with the current uClibc-based toolchains.

[emersion]

glibc only exports strdup when _POSIX_C_SOURCE=200809L

Then report the bug to glibc.

[pcercuei]

I forced-push to a new commit that adds some feature macros in order for struct timespec to be visible on uClibc. The commit is based on 0.12.0, I will need to try with the latest master too.

[emersion]

wlroots has migrated to gitlab.freedesktop.org. This pull request has been moved to:

https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/2493