add an error check

related to PR 13346
fix typesetting for empty reduction relations

closes PR 13346
reference: expand notation section

Also, move it after the language-model section.
repairs for when set_locale() always return NULL

... as it does on Android
add GC-stress mode

Stress mode forces a GC on every N allocation attempts, and it makes
JIT-generated code always take a slow path.

This mode uncovered only a bad test case and some boring start-up
bugs (boring because start-up is deterministic enough that they
never happen), so far.
configure: fix `ar' and `as' inference for cross-compile
work around Android dlsym() bug
add advice on cross-compiling for Android
Fix require/untyped-contract to generate better names in contracts.

Related to PR 13716.
New Racket version 5.3.4.7.
added stepper-complete string constant
raco setup: add --doc-index; raco pkg: use --doc-index

This combination of changes moves the decision about rebuilding
"scribblings/main" and "scribblings/main/user" to `raco setup',
which is in a better position to know whether documentation should
be built at all.
Adding summary mode, quiet program mode and changing tests/eli-tester to cooperate so it adds useful information in summary mode
Clean up struct: and disallow unsupported options

Related to PR 13562
use correct value for (processor-count) on QNX
fix bytecode validator bug

If a function is bound by a `letrec' (or internal definition)
that cannot be simplified to `let' or lifted to a constant or
top-/module-level function, and if the `letrec' binding is used in
a non-application position, and if the function has in its closure
a typed binding (i.e., boxed, fixnum, flonum, or extflonum),
then the validator was incorrectly rejecting the function's
bytecode --- because the validator didn't distinguish between typed
arguments and typed closure content.

File under "surprised that we didn't hit this one earlier".
raco setup: allow foreign-lib and man-page installation

This change hopefully fills out the things that a distribution
can do and that packages should be able to extend.
some random tests to try to stress the immutable hash table implementation
Fix docs for Opaque

Closes PR 13531
Fix race condition in `delay/thread'.

There's mutual dependence between promises and their threads. This may
cause a thread to start running before its promise is fully initialized,
in which case it will be `#<undefined>', which causes errors down the road.

This was the cause of an intermittent failure in the TR test harness.