get platform info from build script

meson.build

@@ -1,21 +1,57 @@
 project(
-  'owdtest',
+  'owdt',
   'c',
   default_options : ['c_std=c17']
 )
 
+eventloop_epoll = 'epoll'
+eventloop_kqueue = 'kqueue'
+
+platform_info = {
+  'linux': {
+    'eventloop': eventloop_epoll,
+  },
+  'freebsd': {
+    'eventloop': eventloop_kqueue,
+  },
+  'openbsd': {
+    'eventloop': eventloop_kqueue,
+  },
+  'netbsd': {
+    'eventloop': eventloop_kqueue,
+  },
+  'dragonfly': {
+    'eventloop': eventloop_kqueue,
+  },
+  'darwin': {
+    'eventloop': eventloop_kqueue,
+  },
+}[target_machine.system()]
+
+eventloop_info = {
+  eventloop_epoll: {
+    'path': 'src/eventloop_epoll.c',
+  },
+  eventloop_kqueue: {
+    'path': 'src/eventloop_kqueue.c',
+  },
+}[platform_info['eventloop']]
+
 sources = [
   'src/main.c',
   'src/server.c',
   'src/client.c',
   'src/str.c',
   'src/eventloop.c',
+  eventloop_info['path'],
 ]
 
 includes = include_directories('include')
 
 args = [
-  '-Wall'
+  '-Wall',
+  '-DOWD_PLATFORM_' + target_machine.system().to_upper(),
+  '-DOWD_EVENTLOOP_' + platform_info['eventloop'].to_upper(),
 ]
 
 executable(