[ELF] Add --remap-inputs= and --remap-inputs-file=

--remap-inputs-file= can be specified multiple times, each naming a
remap file that contains `from-glob=to-file` lines or `#`-led comments.
('=' is used a separator a la -fdebug-prefix-map=)
--remap-inputs-file= can be used to:

* replace an input file. E.g. `"*/libz.so=exp/libz.so"` can replace a resolved
  `-lz` without updating the input file list or (if used) a response file.
  When debugging an application where a bug is isolated to one single
  input file, this option gives a convenient way to test fixes.
* remove an input file with `/dev/null` (changed to `NUL` on Windows), e.g.
  `"a.o=/dev/null"`. A build system may add unneeded dependencies.
  This option gives a convenient way to test the result removing some inputs.

`--remap-inputs=a.o=aa.o` can be specified to provide one pattern without using
an extra file.
(bash/zsh process substitution is handy for specifying a pattern without using
a remap file, e.g. `--remap-inputs-file=<(printf 'a.o=aa.o')`, but it may be
unavailable in some systems. An extra file can be inconvenient for a build
system.)

Exact patterns are tested before wildcard patterns. In case of a tie, the first
patterns wins. This is an implementation detail that users should not rely on.

Co-authored-by: Marco Elver <elver@google.com>
Link: https://discourse.llvm.org/t/rfc-support-exclude-inputs/70070

Reviewed By: melver, peter.smith

Differential Revision: https://reviews.llvm.org/D148859

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