NSS:
* test NSS-specific code with -std=gnu99
* use a recent gcc version from the latest Ubuntu image

Chutney:
* use clang, so we keep one clang Linux job
* keep clang on a fast job, so the overall build finishes quickly

Closes ticket 32500 for 0.3.5.

Merge C_DIALECT_OPTIONS from ticket32500_029 with
other configure options from maint-0.3.5.

Require C99 standards-conforming code in Travis CI, but allow GNU gcc
extensions. Also activates clang's -Wtypedef-redefinition warnings.

Builds some jobs with -std=gnu99, and some jobs without.

Closes ticket 32500.

Install the mingw OpenSSL package in Appveyor. This makes sure that
the OpenSSL headers and libraries match in Tor's Appveyor builds.

(This bug was triggered by an Appveyor image update.)

Fixes bug 32449; bugfix on 0.3.5.6-rc.

Bionic has a recent coccinelle version, which passes our CI tests.

But Bionic (and Xenial) cause permissions errors for chutney.
We'll fix those in 32240.

Part of 31919.

hs_client_purge_state() and hs_cache_clean_as_client() can remove a descriptor
from the client cache with a NEWNYM or simply when the descriptor expires.

Which means that for an INTRO circuit being established during that time, once
it opens, we lookup the descriptor to get the IP object but hey surprised, no
more descriptor.

The approach here is minimalist that is accept the race and close the circuit
since we can not continue. Before that, the circuit would stay opened and the
client wait the SockTimeout.

Fixers #28970.

Signed-off-by: David Goulet <dgoulet@torproject.org>

Closes ticket 32241.

`git merge --strategy ours` to take the 0.3.5 changes for 31001,
and ignore the conflicting 0.2.9 changes.

This build was added in 0.3.5.

We need to mitigate slow scheduling of Travis macOS jobs.

Closes ticket 32177.

Stem from maint-0.3.5, disabled macOS chutney from ticket32177_029.

We need to mitigate slow scheduling of Travis macOS jobs.

Closes ticket 32177.