* Fix sgx porting issues: incorrect compilation flags, porting function impl, document, etc.
* Update bh_platform.c
Add check for function bh_vprintf_sgx: check whether print_function is not NULL.
Remove wasm_export_api.h that may confuse
Implement wasm_runtime_validate_app_str_addr()
Fix bugs of loader and pass more spec cases
Signed-off-by: Weining Lu <weining.x.lu@intel.com>