Add testing code for XCJobs:Export
Make `GCC_SYMBOLS_PRIVATE_EXTERN` as default option for testing
File extension added automatically if absent
Merge pull request #9 from norio-nomura/add-spec-for-export

Add testing code for XCJobs:Export
Merge pull request #11 from kishikawakatsumi/extname

File extension added automatically if absent
Merge pull request #10 from kishikawakatsumi/extern_symbols

Make `GCC_SYMBOLS_PRIVATE_EXTERN` as default option for testing