MachO: Comment fields in the version_min load command.
Darwin: Add assembler directives to create version-min load commands.

Allow object files to be tagged with a version-min load command for iOS
or MacOSX.

Teach macho-dump to understand the version-min load commands for
testcases.

rdar://11337778
MachO: Emit a version-min load command when possible.

When deployment target version information is available, emit it to the
target streamer for inclusion in the object file.

rdar://11337778
Tidy up. Update per naming conventions.

No functional change.