[PATCH v4 00/11] Demangle minimal symbol names in worker threads

[Tom Tromey]

This is v4 of my patch series to demangle minimal symbol names in
worker threads.

v3 was here:

    https://sourceware.org/ml/gdb-patches/2019-05/msg00669.html

This version addresses all review comments, and fixes a few problems.
Some significant changes compared to v3:

* Added a patch to switch gdb's m4 files from sinclude to m4_include.

* Arranged to block signals that are needed by gdb in new threads.
  E.g. this prevents a SIGCHLD from arriving in the wrong thread.

* Arranged for the demangler threads to call sigaltstack.

* Changed the API of parallel_for_each to make the sigaltstack patch
  work in a non-convoluted way.  This also makes it simpler to change
  parallel_for_each to run on top of a thread pool later on, should we
  desire.

* Added a patch to use run_on_main_thread in gdb.post_event, as
  requested.

* Removed the ada_decode patch, as a different version of this has
  landed.

Tested on x86-64 Fedora 28.

Tom