[Issue 22707] New: Windows: LIB env variable for link.exe is overwritten

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=22707

          Issue ID: 22707
           Summary: Windows: LIB env variable for link.exe is overwritten
           Product: D
           Version: D2
          Hardware: All
                OS: Windows
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: kinke at gmx.net

DMD seems to overwrite the LIB env var with the LIB value in the sc.ini config
file, instead of appending (or prepending) that value to the potentially
existing variable (like LDC).

So it's impossible to use LIB to point to a directory containing required libs
for linking, and one has to resort to `-L/LIBPATH:…` business.

The problem seems to be
https://github.com/dlang/dmd/blob/71ba3fa46221daa0539b03ed7e41f454bd6ce326/src/dmd/mars.d#L722;
existing DFLAGS are merged with the config file value in the line above, but
LIB is simply overwritten.

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