Some builds of GCC produce output on both stdout and stderr when --help
--verbose is used.  The 2>&1 redirection caused them to be arbitrarily
interleaved with each other because of stream buffering.  Consequently,
grep failed to match the fvisibility= string in the mixed output, even
though the string was present in GCC's standard output.

This led to silently disabling symbol hiding in some builds of curl.

... causing SIGSEGV while parsing URL with too many globs.
Minimal example:

$ curl $(for i in $(seq 101); do printf '{a}'; done)

Reported-by: Romain Coltel
Bug: https://bugzilla.redhat.com/1340757

Added 8 bug fixes and 5 more contrbutors

(since we just merged two major features)

Included a summary of the checksrc.bat updates and combined two krb5
changes as they should have been implemented at the same time.

As this was introduced in the recent vauth changes and not a prior
release.

Closes #658