Add CMake support for IPOpt

It works for me with the Debian packages for IPOpt.

cmake/modules/AddIPOptFlags.cmake

+function(add_dune_ipopt_flags _targets)
+  if(IPOPT_FOUND)
+    cmake_parse_arguments(ADD_DUNE_IPOPT_FLAGS "OBJECT" "" "" ${ARGN})
+    foreach(_target ${_targets})
+      target_compile_options(${_target} PRIVATE ${DUNE_IPOPT_CFLAGS})
+      if(NOT ADD_DUNE_IPOPT_FLAGS_OBJECT)
+        target_link_libraries(${_target} ${IPOPT_LIBRARY})
+      endif()
+    endforeach(_target ${_targets})
+  endif(IPOPT_FOUND)
+endfunction(add_dune_ipopt_flags)

cmake/modules/CMakeLists.txt

-set(modules "DuneSolversMacros.cmake")
-
-install(FILES ${modules} DESTINATION ${DUNE_INSTALL_MODULEDIR})
+install(FILES
+  DuneSolversMacros.cmake
+  FindIPOpt.cmake
+  AddIPOptFlags.cmake
+  DESTINATION ${DUNE_INSTALL_MODULEDIR})

cmake/modules/DuneSolversMacros.cmake

 # File for module specific CMake tests.
+find_package(IPOpt)
+include(AddIPOptFlags)

cmake/modules/FindIPOpt.cmake

+find_package(PkgConfig REQUIRED)
+include(FindPackageHandleStandardArgs)
+
+pkg_check_modules(IPOPT ipopt)
+find_package_handle_standard_args(Ipopt DEFAULT_MSG IPOPT_FOUND)
+find_library(IPOPT_LIBRARY ipopt HINTS "${IPOPT_LIBDIR}")
+set(HAVE_IPOPT ENABLE_IPOPT)
+
+if(IPOPT_FOUND)
+  set(DUNE_IPOPT_CFLAGS ${IPOPT_CFLAGS} -DENABLE_IPOPT=1)
+  foreach(dir ${PSURFACE_INCLUDE_DIRS})
+    set_property(GLOBAL APPEND PROPERTY ALL_PKG_FLAGS "-I${dir}")
+  endforeach()
+endif(IPOPT_FOUND)