Build i386 for iOS and macOS

Summary: Closes https://github.com/facebook/yoga/pull/391

Reviewed By: emilsjolander

Differential Revision: D4549469

Pulled By: splhack

fbshipit-source-id: 7500b7235218f9a4f564adb36044303dff520fd6

csharp/BUCK

@@ -39,7 +39,9 @@ with allow_unsafe_import():
 
 if os.path.isdir('/Applications/Xcode.app'):
   yoganet_ios_srcs = []
-  for arch in ['iphonesimulator-x86_64', 'iphoneos-arm64', 'iphoneos-armv7']:
+  for arch in [
+    'iphonesimulator-x86_64', 'iphonesimulator-i386', 'iphoneos-arm64', 'iphoneos-armv7'
+  ]:
     name = 'yoganet-' + arch
     yoganet_ios_srcs.append(':' + name)
     genrule(
@@ -61,3 +63,15 @@ if os.path.isdir('/Applications/Xcode.app'):
     cmd = 'lipo $SRCS -create -output $OUT',
     visibility = ['PUBLIC'],
   )
+
+  yoganet_macosx_target = 'csharp:yoganet#macosx-%s,dynamic'
+  genrule(
+    name = 'yoganet-macosx',
+    srcs = [
+      yoga_dep(yoganet_macosx_target % 'x86_64'),
+      yoga_dep(yoganet_macosx_target % 'i386'),
+    ],
+    out = 'libyoga.dylib',
+    cmd = 'lipo $SRCS -create -output $OUT',
+    visibility = ['PUBLIC'],
+  )