Fill in dt_pthread_setname() support for BSD's.

Index: ConfigureChecks.cmake
--- ConfigureChecks.cmake.orig
+++ ConfigureChecks.cmake
@@ -22,6 +22,8 @@ if(HAVE_CPUID_H)
   check_symbol_exists(__get_cpuid "cpuid.h" HAVE___GET_CPUID)
 endif()
 
+check_include_file(pthread_np.h HAVE_PTHREAD_NP_H)
+
 check_include_file(execinfo.h HAVE_EXECINFO_H)
 
 if(OpenMP_FOUND)
