Andrew, I downloaded libsndfile-1.2.2 from:

    https://github.com/libsndfile/libsndfile/releases
(previously from:  http://www.mega-nerd.com/libsndfile/files/libsndfile-1.0.28.tar.gz)

It does not build.  Here is part of the log file:

  static                  libsndfile

...

tar -xJf src/libsndfile-1.2.2.tar.xz   (rebuilt the gz to xz just because previous version was xz)

...

touch /tmp/cinelerra-5.1/thirdparty/../thirdparty/build/libsndfile.source

...

  CONFIGURING libsndfile
...
cd libsndfile* &&   ./configure --disable-shared --enable-static --disable-sqlite --disable-mpeg
...
/bin/bash: ./configure: No such file or directory

...

make[2]: *** [Makefile:373: /tmp/cinelerra-5.1/thirdparty/../thirdparty/build/libsndfile.configure] Error 127

I verified that thirdparty/libsndfile-1.2.2 has files in it but no "configure" file.