build: Add missing include for Dl_info on FreeBSD which is only used

when execinfo is enabled.

src/trap.c:144: error: 'Dl_info' undeclared (first use in this function)
src/trap.c:144: error: expected ';' before 'dli'
cc1: warnings being treated as errors
src/trap.c:187: warning: implicit declaration of function 'dladdr'
src/trap.c:187: error: 'dli' undeclared (first use in this function)

src/trap.c

@@ -33,6 +33,7 @@ char tvh_binshasum[20];
 #include <limits.h>
 #if ENABLE_EXECINFO
 #include <execinfo.h>
+#include <dlfcn.h>
 #endif
 #include <stdio.h>
 #include <stdarg.h>