Problem in signing an enclave library linked with libgmp

Hi,

We're using a Rust library which depends on `rust-gmp` which also depends on `libgmp`. We are able to produce `enclave.so` by linking the `libgmp`. But in the last phase, during the signing process, we get the following error:

```bash
LINK => enclave/enclave.so
mkdir -p bin

0
0
0x40000
0x100000
1
1
0
0
0xFFFFFFFF

[check_symbol_table elfparser.cpp:253] symbol '__gmpz_cmp' is undefined
Symbol table incorrect
The input enclave file is not correct.
Error happened while signing the enclave.
Makefile:134: recipe for target 'bin/enclave.signed.so' failed
make: *** [bin/enclave.signed.so] Error 255
```

Is there a solution to this problem?
@dingelish

Start with the Makefile target for bin/enclave.signed.so and the signing output, then trace how enclave/enclave.so is linked with rust-gmp and libgmp. Investigate why __gmpz_cmp remains undefined in the ELF symbol table; done means the enclave signs successfully without the Symbol table incorrect error.

Written by the indexing model from the issue text.