es2gears: do not define _GNU_SOURCE
We're defining it from the build-system now, and doing both gives us a compiler-warning. Let's drop doing it here.
Fixes: af947da7 ("meson: add various preprocessor defines for various OSes")
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We're defining it from the build-system now, and doing both gives us a compiler-warning. Let's drop doing it here.
Fixes: af947da7 ("meson: add various preprocessor defines for various OSes")