[Issue 24423] New: Support dmd specific CC environment variable

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24423

          Issue ID: 24423
           Summary: Support dmd specific CC environment variable
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: alphaglosined at gmail.com

For Posix it may be a good idea to support a second (with priority) environment
variable specific to dmd that acts as $CC does.

This can be useful when using dmd as a C compiler (where dmd still needs the C
compiler to link).

That way you can do this, instead of modifying the build script wrt. the
compiler itself.

```sh
DMD_CC=$CC
CC=dmd
```

https://forum.dlang.org/thread/chddxuxyhdbtorvprnzu@forum.dlang.org

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