Build native library with BUCK for .NET (Mono, Xamarin)

Examples:

- macOS on macOS (Mono, Xamarin.Mac, Unity)
  - `buck build //csharp:yoganet#shared,default` -> `libyoga.dylib`
- Android (Xamarin.Android, Unity)
  - `buck build //csharp:yoganet#shared,android-armv7` -> `libyoga.so`
- iOS (Xamarin.iOS, Unity)
  - `buck build //:yoga#static,iphoneos-arm64` -> `libyoga.a`
  - `buck build //csharp:yoganet#static,iphoneos-arm64` -> `libyoganet.a`

BUCK

@@ -7,14 +7,6 @@
 
 include_defs('//YOGA_DEFS')
 
-BASE_COMPILER_FLAGS = [
-  '-fno-omit-frame-pointer',
-  '-fexceptions',
-  '-Wall',
-  '-Werror',
-  '-O3',
-]
-
 GMOCK_OVERRIDE_FLAGS = [
   # gmock does not mark mocked methods as override, ignore the warnings in tests
   '-Wno-inconsistent-missing-override',

YOGA_DEFS

@@ -17,6 +17,14 @@ CXX_LIBRARY_WHITELIST = [
   '//java:jni',
 ]
 
+BASE_COMPILER_FLAGS = [
+  '-fno-omit-frame-pointer',
+  '-fexceptions',
+  '-Wall',
+  '-Werror',
+  '-O3',
+]
+
 def yoga_dep(dep):
   return '//' + dep
 

csharp/BUCK

@@ -5,6 +5,10 @@
 # LICENSE file in the root directory of this source tree. An additional grant
 # of patent rights can be found in the PATENTS file in the same directory.
 
+include_defs('//YOGA_DEFS')
+
+COMPILER_FLAGS = BASE_COMPILER_FLAGS + ['-std=c++11']
+
 csharp_library(
   name = 'yogalibnet46',
   dll_name = 'Facebook.Yoga.dll',
@@ -18,3 +22,14 @@ csharp_library(
   framework_ver = 'net45',
   srcs = glob(['**/*.cs']),
 )
+
+cxx_library(
+  name = 'yoganet',
+  soname = 'libyoga.$(ext)',
+  srcs = glob(['Yoga/YGInterop.cpp']),
+  compiler_flags = COMPILER_FLAGS,
+  link_style = 'static',
+  link_whole = True,
+  deps = [yoga_dep(':yoga')],
+  visibility = ['PUBLIC'],
+)