mach-o: no imports on stripped binary

goblin cannot find the interpreter of a stripped binary, and `imports()` returns empty vector. However, `nm -um` could still list the undefined symbol of the binary, and the corresponding depend dylibs.

Start by reproducing the issue with a stripped Mach-O binary and compare goblin's empty imports() result with nm -um, which lists the undefined symbol and dependent dylibs. Done means goblin can identify the interpreter and return the relevant undefined symbols and dependent dylibs for stripped binaries.

Written by the indexing model from the issue text.