[Bug debug/68848] allow -fdebug-prefix-map to read OLD prefix from environment (improve reproducibility)

[dkg at fifthhorseman dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68848

Daniel Kahn Gillmor <dkg at fifthhorseman dot net> changed:

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--- Comment #1 from Daniel Kahn Gillmor <dkg at fifthhorseman dot net> ---
Created attachment 37001
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=37001&action=edit
allow reading OLD argument to -fdebug-prefix-map from environment (using ENV:
prefix)

I'm attaching an updated patch that uses an "ENV:" prefix instead of a literal
"$", because the "$" is messy to pass through a complex build chain without a
lot of escaping.

So the reproducible use case would be something like:

  export SOURCE_BUILD_DIR="$(pwd)"
  gcc -fdebug-prefix-map=ENV:SOURCE_BUILD_DIR=/usr/src