MFC r308772: crunchide: report explicit error for combined string table

MFC r308772: crunchide: report explicit error for combined string table

Some tools produce objects with a combined strtab and shstrtab.
These objects are not supported by crunchide since it rewrites the
symtab and strtab to "hide" symbols. This invalidates section header
offsets into a combined strtab/shstrtab.

In the future we could support these objects (by ensuring that we retain
unmodified section name strings in the output .strtab, and then rewriting
each section header's sh_name).

git-svn-id: svn://svn.freebsd.org/base/stable/10@309077 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f