OpenSystemsDevelopment / qpdf

Configure emacs and clang-format 15 to the coding style I am choosing
for qpdf.

I'm not sure why this is needed now and wasn't needed before since the
cmake changes have been in main for a while and there don't appear to
be recent changes to the appimage build tools.

This change adds to lib directory to LD_LIBRARY_PATH so the appimage
tools' ldd check will pass. This is an appropriate change since the
directory that is added will be in the standard load path when
installed.

Also add a pkg-config runtime test that would have caught the error.

Some platforms need it for atomic<long long> but not for atomic<int>.

The executables that libtool built invoked the underlying binary with
an "lt-" prefix. The code contained numerous workarounds for testing,
which can now be removed.

Handle various options that were handled in Makefile code.