* mach-o.c (bfd_mach_o_read_main)
(bfd_mach_o_read_source_version): New functions.
(bfd_mach_o_read_command): Handle BFD_MACH_O_LC_DATA_IN_CODE,
BFD_MACH_O_LC_DYLIB_CODE_SIGN_DRS, BFD_MACH_O_LC_MAIN,
BFD_MACH_O_LC_SOURCE_VERSION.
* mach-o.h (bfd_mach_o_main_command)
(bfd_mach_o_source_version_command): New types.
(bfd_mach_o_load_command): Add fields for these new types.