GIO tests fail on FreeBSD CI with: Unexpected error from C library during 'pthread_mutex_lock': Invalid argument

Makes it difficult to automatically merge MRs when CI passes, and will make it harder to notice when something really breaks on FreeBSD.

Exhibit A

174/258 glib:gio / appinfo                      FAIL     0.32 s (killed by signal 6 SIGABRT)
178/258 glib:gio / gdbus-auth                   FAIL     0.06 s (killed by signal 6 SIGABRT)
179/258 glib:gio / gdbus-bz627724               FAIL     0.14 s (killed by signal 6 SIGABRT)
181/258 glib:gio / gdbus-connection             FAIL     0.24 s (killed by signal 6 SIGABRT)
194/258 glib:gio+slow / gdbus-threading         FAIL     0.26 s (killed by signal 6 SIGABRT)

Exhibit B1, B2, B3, B4 (same MR, repeated retries that all failed)

174/258 glib:gio / appinfo                      FAIL     0.33 s (killed by signal 6 SIGABRT)

Exhibit C

174/258 glib:gio / appinfo                      FAIL     0.32 s (killed by signal 6 SIGABRT)

Exhibit D

174/258 glib:gio / appinfo                      FAIL     0.31 s (killed by signal 6 SIGABRT)
194/258 glib:gio+slow / gdbus-threading         FAIL     9.67 s (killed by signal 5 SIGTRAP)

CCing: @lantw @xclaesse @jmatthew

How does one go about setting up the FreeBSD image being used locally using Docker to debug this?

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The appinfo failures are believed to be #1601 (closed). The gdbus-threading failures are #1515 (closed). This issue report has been repurposed to represent the other failures in Exhibit A.