/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/stdc/ is in libphobos-5-dev 5.5.0-12ubuntu1.
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..
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/stdc/complex.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/stdc/config.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/stdc/ctype.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/stdc/errno.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/stdc/fenv.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/stdc/float_.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/stdc/inttypes.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/stdc/limits.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/stdc/locale.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/stdc/math.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/stdc/signal.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/stdc/stdarg.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/stdc/stddef.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/stdc/stdint.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/stdc/stdio.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/stdc/stdlib.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/stdc/string.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/stdc/tgmath.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/stdc/time.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/stdc/wchar_.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/stdc/wctype.d