Tweak the "ignoring return value" fortify workaround for readlinkat.

We zero the buffer and if the link read fails that's left alone, so
it's ok for the symlink not to be there. Unfortunately, typecasting the
return value to (void) doesn't shut up gcc, and having an if(); with the
semicolon on the same line doesn't shut up llvm. (The semicolon on a new
line would, but C does not have significant whitespace and I'm not going
to humor llvm if it plans to start.)

So far, empty curly brackets consistently get the warning to shut up.
Android-related roadmap.html updates.

most notably:

* Android switched to mksh several releases ago.

* system/core/reboot is Android's reboot(1) (and sdcard is how
emulated sdcards work in production, not a testing thing).

* I removed all the "apparently unused" tools from the tree, since
they were all actually unused with the exception of lsusb which people
would build as/when they needed it. (which may need resurrecting when
they come back and find there's no "lsusb -v" in toolbox.)