This is from src/ar, the third CU:
Ah! GCC actually emits DW_AT_comp_dir only if there are any directory or
file table entries that would rely on it (i.e. are not absolute). OK.
Maybe there was some default conversion everybody uses when dealing
std::string vs const char* where there can be NULLs. But it seems not. I
learned a lot about conversions, copy constructors and using gdb to
catch exceptions though.