Generate LC_FUNCTION_STARTS load command.

This load command generates data in the LINKEDIT section which
is a list of ULEB128 delta's to all of the functions in the __text section.

It is then 0 terminated and pointer aligned to pad.

ld64 exposes the -function-starts and no-function-starts cmdline options
to override behaviour from the defaults based on file types.

rdar://problem/24472630

llvm-svn: 260188