[Issue 15012] Druntime Makefile whitelists compilers

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=15012

--- Comment #1 from Martin Nowak <code at dawg.eu> ---
This is the same as in the phobos makefile, so it's kind of surprising that you
only have an issue with druntime.
https://github.com/D-Programming-Language/phobos/blob/88fc63d8d3d47ded732e801d4ccacec21eccb8f2/posix.mak#L96

We could indeed check against the basename of $(CC) and you can explicitly set
$(CFLAGS) for other compilers.
https://github.com/D-Programming-Language/druntime/pull/1378
https://github.com/D-Programming-Language/phobos/pull/3633

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