rework SystemExec - use vfork wrapper (and lots of related stuff)

libs/vfork/wscript

@@ -0,0 +1,28 @@
+#!/usr/bin/env python
+from waflib.extras import autowaf as autowaf
+from waflib import TaskGen
+import os
+import sys
+
+# Mandatory variables
+top = '.'
+out = 'build'
+
+def options(opt):
+    autowaf.set_options(opt)
+
+def configure(conf):
+    conf.load('compiler_c')
+    autowaf.configure(conf)
+
+def build(bld):
+    if bld.env['build_target'] == 'mingw':
+        return
+    obj = bld (features = 'c cprogram')
+    obj.source = 'exec_wrapper.c'
+    obj.target = 'ardour-exec-wrapper'
+    obj.install_path = os.path.join(bld.env['LIBDIR'], 'ardour3/vfork')
+    obj.defines = [
+            '_POSIX_SOURCE',
+            '_XOPEN_SOURCE=700',
+    ]