Define _POSIX_C_SOURCE globally and detect supported warnings

log.c

@@ -1,4 +1,3 @@
-#define _POSIX_C_SOURCE 199506L
 #include <errno.h>
 #include <stdarg.h>
 #include <stdio.h>

loop.c

@@ -1,4 +1,3 @@
-#define _POSIX_C_SOURCE 200809L
 #include <limits.h>
 #include <string.h>
 #include <stdbool.h>

main.c

@@ -1,4 +1,3 @@
-#define _POSIX_C_SOURCE 200809L
 #include <assert.h>
 #include <ctype.h>
 #include <errno.h>

meson.build

@@ -11,20 +11,18 @@ project(
 	],
 )
 
-add_project_arguments(
-	[
-		'-Wno-unused-parameter',
-		'-Wno-unused-result',
-		'-Wundef',
-		'-Wvla',
-	],
-	language: 'c',
-)
-
 cc = meson.get_compiler('c')
 
-is_freebsd = host_machine.system().startswith('freebsd')
+add_project_arguments('-D_POSIX_C_SOURCE=200809L', language: 'c')
+
+add_project_arguments(cc.get_supported_arguments([
+	'-Wno-unused-parameter',
+	'-Wno-unused-result',
+	'-Wundef',
+	'-Wvla',
+]), language: 'c')
 
+is_freebsd = host_machine.system().startswith('freebsd')
 if is_freebsd
 	add_project_arguments('-D_C11_SOURCE', language: 'c')
 endif

password-buffer.c

@@ -1,4 +1,3 @@
-#define _POSIX_C_SOURCE 200809L
 #include "password-buffer.h"
 #include "log.h"
 #include "swaylock.h"

pool-buffer.c

@@ -1,4 +1,3 @@
-#define _POSIX_C_SOURCE 200809L
 #include <assert.h>
 #include <cairo/cairo.h>
 #include <errno.h>

shadow.c

@@ -1,3 +1,4 @@
+#undef _POSIX_C_SOURCE
 #define _XOPEN_SOURCE // for crypt
 #include <assert.h>
 #include <pwd.h>