[vte] build: Try to fix pwrite detection on non-glibc systems

[Christian Persch <chpe src gnome org>]

commit 8c4b920cba056d1100a15eae5f4aa02c92452dcb
Author: Christian Persch <chpe src gnome org>
Date:   Mon Apr 18 19:39:01 2022 +0200

    build: Try to fix pwrite detection on non-glibc systems
    
    Define _POSIX_C_SOURCE for POSIX 2008.

 meson.build | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/meson.build b/meson.build
index abe7e8fd..2d35be83 100644
--- a/meson.build
+++ b/meson.build
@@ -204,6 +204,7 @@ endif
 
 # FIXME AC_USE_SYSTEM_EXTENSIONS also supported non-gnu systems
 config_h.set10('_GNU_SOURCE', true)
+config_h.set('_POSIX_C_SOURCE', '200809L')
 
 # Check headers
 
@@ -386,7 +387,7 @@ foreach func: check_functions
     __code,
     args: [
       '-D_GNU_SOURCE',
-      '-D_XOPEN_SOURCE',
+      '-D_POSIX_C_SOURCE=200809L',
     ],
     dependencies: __deps,
     name: __name,