The gnatdroid cross-compilers (*BSD => Android) were the last two users
of gcc-aux (gcc 4.9 Ada compiler). They are now based on gcc6-aux.
The Android NDK release 11 just came out with support for Android API 23
(Marshmellow) so now gnatdroid supports it. I removed API 8 and 9
(Froyo and Gingerbread) from gnatdroid-armv7. Froyo currently is installed
on less than 0.1% of Android devices, and Gingerbread is dropping under 2%
soon. Many sysroot distfiles were re-rolled to gain required headers, so
a distfiles subdirectory was added as well.
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