We need to include the execinfo.h file when testing if backtrace is available; otherwise, we may well find that the OS has these functions, but not from a header file of that name, and then the build fails in exceptions.c when we include it.
We need to include the execinfo.h file when testing if backtrace is available; otherwise, we may well find that the OS has these functions, but not from a header file of that name, and then the build fails in exceptions.c when we include it.

git-svn-id: 6e74a02f85675cec270f5d931b0f6998666294a3@24036 d31e2699-5ff4-0310-a27c-f18f2fbe73fe

ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot