Test fixes from rollup

Closes #13396 (rustc: Remove absolute rpaths)
Closes #13394 (sync: remove unsafe and add Send+Share to Deref (enabled by autoderef vtables))
Closes #13389 (Made libflate functions return Options instead of outright failing)
Closes #13388 (doc: Document flavorful variations of paths)
Closes #13387 (Register new snapshots)
Closes #13386 (std: Add more docs for ptr mod)
Closes #13384 (Tweak crate loading to load less metadata)
Closes #13382 (fix ~ZeroSizeType rvalues)
Closes #13378 (Update tidy script, replace XXX with FIXME)
Closes #13377 (std: User a smaller stdin buffer on windows)
Closes #13369 (Fix spelling errors in comments.)
Closes #13314 (Made 'make install' include libs for additional targets)
Closes #13278 (std: make vec!() macro handle a trailing comma)
Closes #13276 (Add test for #11881)