d: Merge upstream dmd 5fc1806cd.

d: Merge upstream dmd 5fc1806cd.

Backports the OutBuffer interface from upstream dmd master, removing
another difference this and the self-hosted D branch that is purely
refactoring, and doesn't introduce any mechanical changes.

Reviewed-on: https://github.com/dlang/dmd/pull/11302

gcc/d/ChangeLog:

	* dmd/MERGE: Merge upstream dmd 5fc1806cd.
	* d-lang.cc (d_parse_file): Use peekChars to get string representation
	of OutBuffer data.