Enhance build-time configuration

[jethrogb]

Currently, the following information is injected into the binary at build time (post-link):

• Symbols
  • ENCLAVE_SIZE
  • RELA, RELACOUNT
  • HEAP_BASE, HEAP_SIZE
  • CFGDATA_BASE
  • EH_FRM_HDR_BASE, EH_FRM_HDR_SIZE
  • TEXT_BASE, TEXT_SIZE
  • DEBUG
• TCSes

1. Consider adding a more generic mechanism for information injection.
   • Consider making SGX_INEFFECTIVE_ERROR configurable.
2. Consider adding additional infrastructure for run-time introspection (say, obtaining the number of TCSes, possibly even their addresses).
3. Consider making DEBUG more than just a single bit.
   • Does a panic output anything?
   • Are backtraces enabled?
   • Is the enclave state saved on enclave abort?
   • ...?
4. EH_FRM_HDR_BASE, EH_FRM_HDR_SIZE, TEXT_BASE, TEXT_SIZE may be elided if the enclave is compiled with panic = "abort". Maybe these should be defined in panic_unwind instead of std?

Related #16, #84