[sysprof] build: specify -D_DARWIN_C_SOURCE on darwin

[Christian Hergert <chergert src gnome org>]

commit c82b0a1677bb64c5c5e8edd6eaf0823c493abd3f
Author: Christian Hergert <chergert redhat com>
Date:   Mon Nov 16 13:58:42 2020 -0800

    build: specify -D_DARWIN_C_SOURCE on darwin
    
    Needed for access to things like RTLD_NEXT

 meson.build | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/meson.build b/meson.build
index c4d505e..590b98a 100644
--- a/meson.build
+++ b/meson.build
@@ -92,6 +92,9 @@ global_c_args = [
   '-D_GNU_SOURCE',
   '-D_POSIX_C_SOURCE=200809L',
 ]
+if host_machine.system() == 'darwin'
+  global_c_args += ['-D_DARWIN_C_SOURCE']
+endif
 test_c_args = [
   '-Wcast-align',
   '-Wdeclaration-after-statement',