[llvm-readelf]Revert --dyn-symbols behaviour to make it GNU compatible, and add new --hash-symbols switch for old behaviour

In r287786, the behaviour of --dyn-symbols in llvm-readelf (but not
llvm-readobj) was changed to print the dynamic symbols as derived from
the hash table, rather than to print the dynamic symbol table contents
directly. The original change was initially submitted without review,
and some comments were made on the commit mailing list implying that the
new behavious is GNU compatible. I argue that it is not:

  1) It does not include a null symbol.
  2) It prints the symbols based on an order derived from the hash
     table.
  3) It prints an extra column indicating which bucket it came from.
     This could break parsers that expect a fixed number of columns,
     with the first column being the symbol index.
  4) If the input happens to have both .hash and .gnu.hash section, it
     prints interpretations of them both, resulting in most symbols
     being printed twice.
  5) There is no way of just printing the raw dynamic symbol table,
     because --symbols also prints the static symbol table.

This patch reverts the --dyn-symbols behaviour back to its old behaviour
of just printing the contents of the dynamic symbol table, similar to
what is printed by --symbols. As the hashed interpretation is still
desirable to validate the hash table, it puts it under a new switch
"--hash-symbols". This is a no-op on all output forms except for GNU
output style for ELF. If there is no hash table, it does nothing,
unlike the previous behaviour which printed the raw dynamic symbol
table, since the raw dynsym is available under --dyn-symbols.

The yaml input for the test is based on that in
test/tools/llvm-readobj/demangle.test, but stripped down to the bare
minimum to provide a valid dynamic symbol.

Note: some LLD tests needed updating. I will commit a separate patch for
those.

Reviewed by: grimar, rupprecht

Differential Revision: https://reviews.llvm.org/D56910

llvm-svn: 351789