Speeding up importing Phobos files

[KnightMare]

>
> I honestly doubt it would improve compilation time that much. 
> Reading files from the filesystem is pretty fast, compared to 
> the rest of the stuff the compiler has to do afterwards.
>

need to search for existing files in dir-tree with some templates 
"datetime.d*" for each folder in -I.

I tried compile (in Windows) one small program from today issue 
https://issues.dlang.org/show_bug.cgi?id=19947 under Procmon.exe 
(tool from SysInternals that allow to see what doing some process 
with Net,FS,Registry,Process&Threads). Result for FileSystem only 
is:
3497 requests to FS for create/open,query,close,read/write (libs 
and dll counted too)
768! requests just "not found" (dlls and libs counted too)

2nd try with option "-c" - compile only (no linking):
2693 requests to FS
727 reqs are "not found"

so for clear benchmark need to compare compilation some middle 
program (without any dub packages coz they add mor path for 
searching maybe N! factorial) with SSD and with RAM-disk, imo we 
can win 1-2secs for compilation