[OCaml] Replace ctypes.foreign with ctypes in META file

[alan]

Summary

ctypes.foreign is only necessary for tests. This change is mainly
for the benefit of people packaging the OCaml bindings.

[alan]

See discussion at https://github.com/kit-ty-kate/llvm-dune/pull/11.

[nikic]

LGTM

llvm/bindings/ocaml/llvm/META.llvm.in

package "bitwriter" (
     requires = "llvm,unix"
     version = "@PACKAGE_VERSION@"
     description = "Bitcode writer for LLVM"
     archive(byte) = "llvm_bitwriter.cma"
     archive(native) = "llvm_bitwriter.cmxa"
 )
 
 package "executionengine" (
-    requires = "llvm,llvm.target,ctypes.foreign"
+    requires = "llvm,llvm.target,ctypes"
     version = "@PACKAGE_VERSION@"
     description = "JIT and Interpreter for LLVM"
     archive(byte) = "llvm_executionengine.cma"
     archive(native) = "llvm_executionengine.cmxa"
 )
 
 package "debuginfo" (
     requires = "llvm"

llvm/test/Bindings/OCaml/executionengine.ml

 (* RUN: rm -rf %t && mkdir -p %t && cp %s %t/executionengine.ml
- * RUN: %ocamlc -g -w +A -thread -package llvm.executionengine -linkpkg %t/executionengine.ml -o %t/executable
+ * RUN: %ocamlc -g -w +A -thread -package ctypes.foreign,llvm.executionengine -linkpkg %t/executionengine.ml -o %t/executable
  * RUN: %t/executable
- * RUN: %ocamlopt -g -w +A -thread -package llvm.executionengine -linkpkg %t/executionengine.ml -o %t/executable
+ * RUN: %ocamlopt -g -w +A -thread -package ctypes.foreign,llvm.executionengine -linkpkg %t/executionengine.ml -o %t/executable
  * RUN: %t/executable
  * REQUIRES: native
  * XFAIL: vg_leak
  *)
 
 open Llvm
 open Llvm_executionengine
 open Llvm_target