[Issue 12341] Add EXTRA_C_SOURCES to autotester

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=12341

RazvanN <razvan.nitu1305 at gmail.com> changed:

           What    |Removed                     |Added
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             Status|NEW                         |RESOLVED
                 CC|                            |razvan.nitu1305 at gmail.com
         Resolution|---                         |WORKSFORME

--- Comment #2 from RazvanN <razvan.nitu1305 at gmail.com> ---
I would argue this is not needed anymore since the compiler can already
identify .c source files. Therefore, we can use EXTRA_SOURCES directly.

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