[symbolizer] Change reaction on invalid input

If llvm-symbolizer finds a malformed command, it echoes it to the
standard output. New versions of binutils (starting from 2.39) allow to
specify an address by a symbols. Implementation of this feature in
llvm-symbolizer makes the current reaction on invalid input
inappropriate. Almost any invalid command may be treated as a symbol
name, so the right reaction should be "symbol not found" in such case.

The exception are commands that are recognized but have incorrect
syntax, like "FILE:FILE:". The utility must produce descriptive
diagnostic for such input and route it to the stderr.

This change implements the new reaction on invalid input and is a
prerequisite for implementation of symbol lookup in llvm-symbolizer.

Differential Revision: https://reviews.llvm.org/D157210