Add more POSIX compliance macros to fix uClibc support

- Add POSIX 1993.09 compliance macro in source files that use
  "struct timespec";
- Add POSIX 2001.12 compliance macro in source files that use
  "struct sigaction" and the SA_SIGINFO macro, or the fchmod()
  function;
- Add POSIX 2008.09 compliance macro in source files that use the
  getline() function.

These compliance macros are enough for wlroots to compile with the
git-master version of uClibc-ng.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>

backend/wayland/output.c

@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <assert.h>
 #include <stdint.h>
 #include <stdio.h>