Add include dirs to the CGO command line arguments (#134)

Summary:
X-link: facebook/buck2#134

Pull Request resolved: #8

X-link: facebook/ocamlrep#23

Without the include dirs, the cgo command won't be able to find the header files causing `buck2 build` to fail.

Reviewed By: krallin

Differential Revision: D44788778

fbshipit-source-id: d1ed1a8ec2463aaba615844c0a3ff54158c1dc69

go/cgo_library.bzl

@@ -64,6 +64,7 @@ def _cgo(
 
     pre = cxx_merge_cpreprocessors(ctx, own_pre, inherited_pre)
     pre_args = pre.set.project_as_args("args")
+    pre_include_dirs = pre.set.project_as_args("include_dirs")
 
     gen_dir = "cgo_gen"
 
@@ -96,6 +97,7 @@ def _cgo(
     args.add(cmd_args(go_srcs[0].as_output(), format = "--output={}/.."))
     args.add(cmd_args(cxx_toolchain.c_compiler_info.preprocessor, format = "--cpp={}"))
     args.add(cmd_args(pre_args, format = "--cpp={}"))
+    args.add(cmd_args(pre_include_dirs, format = "--cpp={}"))
     args.add(srcs)
 
     argsfile = ctx.actions.declare_output(paths.join(gen_dir, ".cgo.argsfile"))