d: Merge upstream dmd 8508c4e68.

d: Merge upstream dmd 8508c4e68.

Fixes a performance bug where 'static foreach' would take an
exponentially long time to expand during CTFE.

In the following example:

    static foreach (i; 0..30000) {}

Compilation time had been reduced from around 40 to 0.08 seconds.
Memory consumption is also reduced from 3.5GB to 55MB.

Reviewed-on: https://github.com/dlang/dmd/pull/11335

gcc/d/ChangeLog:

	* dmd/MERGE: Merge upstream dmd 8508c4e68.