title: How to add *.i files in bazel BUILD script file
body: <p>I want to add <strong>features2d</strong> into the build script for building opencv with bazel. <a href="https://github.com/ApolloAuto/apollo/blob/master/third_party/opencv2.BUILD" rel="nofollow noreferrer">Here</a> is the build script which this module to be added. </p>
  
  <p>I was able to add a few other modules except for <strong>features2d</strong> because inside this module it consists of some *.i files (<a href="https://github.com/opencv/opencv/tree/2.4.13.2/modules/features2d/src" rel="nofollow noreferrer">https://github.com/opencv/opencv/tree/2.4.13.2/modules/features2d/src</a>)</p>
  
  <p>Problem is that there is no rule so as to include *.i in the src directory. </p>
  
  <pre><code>cc_library(
      name = "features2d",
      srcs = glob(["modules/features2d/src/**/*.cpp"]),
      hdrs = glob([
          "modules/features2d/src/**/*.hpp",
          "modules/features2d/src/**/*.h",
          "modules/features2d/include/**/*.hpp",
          "modules/features2d/include/**/*.h"
      ]) + [
          ":module_includes",
      ],
      includes = [
          "modules/features2d/include",
      ],
      visibility = ["//visibility:public"],
      deps = [
          ":imgproc",
          ":flann",
      ],
  )
  </code></pre>
  
  <p>This is the error is trowing: </p>
  
  <pre><code>@opencv2//:modules/features2d/src/generated_32.i' does not produce any cc_library srcs files (expected .cc, .cpp, .cxx, .c++, .C, .c, .h, .hh, .hpp, .hxx, .inc, .S, .s, .asm, .a, .lib, .pic.a, .lo, .pic.lo, .so, .dylib, .dll, .o or .pic.o).
  </code></pre>
  
  <p>If anybody has an idea how this can be done, really helpful. </p>