patch to disable libexecinfo / execinfo.h; seems it can be picked up
on ports-gcc arches.

Index: Source/kwsys/CMakeLists.txt
--- Source/kwsys/CMakeLists.txt.orig
+++ Source/kwsys/CMakeLists.txt
@@ -507,7 +507,7 @@ if(KWSYS_USE_SystemInformation)
     set_property(SOURCE SystemInformation.cxx APPEND PROPERTY
       COMPILE_DEFINITIONS KWSYS_CXX_HAS_RLIMIT64=1)
   endif()
-  if(UNIX AND NOT KWSYS_NO_EXECINFO)
+  if(UNIX AND NOT KWSYS_NO_EXECINFO AND NOT (CMAKE_SYSTEM MATCHES "OpenBSD"))
     include(CheckIncludeFileCXX)
     # check for simple stack trace
     # usually it's in libc but on FreeBSD
