meson: Fixes needed to build on Android (#402)

* meson: add support for android/ios host_system

* build: include ifaddrs.c definition for android
diff --git a/meson.build b/meson.build
index 763edf9..7185094 100644
--- a/meson.build
+++ b/meson.build
@@ -56,7 +56,7 @@
 
 # OS-specific settings
 system = host_machine.system()
-if system == 'linux'
+if ['linux', 'android'].contains(system)
     add_project_arguments([
         '-D__Userspace_os_Linux',
         '-D_GNU_SOURCE',
@@ -68,7 +68,7 @@
     ] + compiler.get_supported_arguments([
         '-Wno-address-of-packed-member',
     ]), language: 'c')
-elif system == 'darwin'
+elif ['darwin', 'ios'].contains(system)
     add_project_arguments([
             '-D__Userspace_os_Darwin',
             '-U__APPLE__',
diff --git a/usrsctplib/meson.build b/usrsctplib/meson.build
index c1a6656..8cb481c 100644
--- a/usrsctplib/meson.build
+++ b/usrsctplib/meson.build
@@ -12,6 +12,9 @@
     'user_recv_thread.c',
     'user_socket.c',
 ])
+if system == 'android'
+    sources += files('ifaddrs.c')
+endif
 
 subdir('netinet')
 subdir('netinet6')