Core dump support

Currently, the core dump file doesn't give much useful information. For example, the following code in enclave:

```c
int get_number() {
int *p = reinterpret_cast(0xdeadbeef);
return *p;
}
```

If you run with `sgx-gdb`, that's fine, you can see the line number:

```
(gdb) r
Starting program: ./app
...
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff5800515 in get_number () at Enclave/Enclave.cpp:6
6 return *p;
(gdb) bt
#0 0x00007ffff5800515 in get_number () at Enclave/Enclave.cpp:6
intel/confidential-computing.sgx#1 0x00007ffff58004f7 in sgx_get_number (pms=0x7fffffffdee0) at Enclave/Enclave_t.c:31
intel/confidential-computing.sgx#2 0x00007ffff5800b30 in do_ecall ()
intel/confidential-computing.sgx#3 0x00007ffff5800988 in enter_enclave ()
intel/confidential-computing.sgx#4 0x00007ffff5801976 in enclave_entry ()
intel/confidential-computing.sgx#5 0x00007ffff7bbe2a2 in __morestack () from /usr/lib/libsgx_urts.so
intel/confidential-computing.sgx#6 0x00007ffff7bc364e in do_ecall(int, void const*, void const*, CTrustThread*) () from /usr/lib/libsgx_urts.so
intel/confidential-computing.sgx#7 0x00007ffff7bc07e9 in CEnclave::ecall(int, void const*, void*) () from /usr/lib/libsgx_urts.so
intel/confidential-computing.sgx#8 0x00007ffff7bc19d8 in sgx_ecall () from /usr/lib/libsgx_urts.so
intel/confidential-computing.sgx#9 0x00000000004007a4 in get_number (eid=2, retval=0x7fffffffdf18) at App/Enclave_u.c:19
intel/confidential-computing.sgx#10 0x000000000040088b in main (argc=1, argv=0x7fffffffe418) at App/App.cpp:21
```

But if you run it then look into the core dump file, you can only get:

```
Core was generated by `./app'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0 __GI_raise (sig=) at ../sysdeps/unix/sysv/linux/raise.c:58
58 ../sysdeps/unix/sysv/linux/raise.c: No such file or directory.
(gdb) bt
#0 __GI_raise (sig=) at ../sysdeps/unix/sysv/linux/raise.c:58
intel/confidential-computing.sgx#1 0x00007fc975ee3492 in sig_handler(int, siginfo_t*, void*) () from /usr/lib/libsgx_urts.so
intel/confidential-computing.sgx#2
intel/confidential-computing.sgx#3 0x00007fc975ede2ed in __morestack () from /usr/lib/libsgx_urts.so
intel/confidential-computing.sgx#4 0x00007fc975ee364e in do_ecall(int, void const*, void const*, CTrustThread*) () from /usr/lib/libsgx_urts.so
intel/confidential-computing.sgx#5 0x00007fc975ee07e9 in CEnclave::ecall(int, void const*, void*) () from /usr/lib/libsgx_urts.so
intel/confidential-computing.sgx#6 0x00007fc975ee19d8 in sgx_ecall () from /usr/lib/libsgx_urts.so
intel/confidential-computing.sgx#7 0x00000000004007a4 in get_number (eid=2, retval=0x7ffda235faa8) at App/Enclave_u.c:19
intel/confidential-computing.sgx#8 0x000000000040088b in main (argc=1, argv=0x7ffda235ffa8) at App/App.cpp:21
```

Is there any chance to enhance the core dump file support? Thanks!