action.c: add _POSIX_C_SOURCE

...to compile cleanly with musl on Void Linux and avoid:

```
[9/58] Compiling C object labwc.p/src_action.c.o
../src/action.c: In function 'actions_run':
../src/action.c:204:4: warning: implicit declaration of function 'kill' [-Wimplicit-function-declaration]
  204 |    kill(getpid(), SIGHUP);
      |    ^~~~
[58/58] Linking target labwc
```

Reported-by: @M4lin

diff --git a/src/action.c b/src/action.c
index c2a0566c5dc963edf54bd14b10c7ce2a7d5280d8..0e5d181f47a09444806c374735c4f7254ec876f7 100644 (file)
--- a/src/action.c
+++ b/src/action.c
@@ -1,4 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0-only
+#define _POSIX_C_SOURCE
 #include <strings.h>
 #include <wlr/util/log.h>
 #include <signal.h>