Adding ILRepack tool for .NET builds

Author: jimevans

third_party/dotnet/ilrepack/BUCK

@@ -0,0 +1,10 @@
+genrule(
+  name = 'ilrepack',
+  srcs = ['ILRepack.exe'],
+  out = 'ILRepack.exe',
+  cmd = 'copy %SRCS% %OUT%',
+  executable = True,
+  visibility = [
+    'PUBLIC'
+  ]
+)