OpenSystemsDevelopment / qpdf

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.

Files are copied into the build area rather than left in the source
tree, and the test suite looks for them there. Also remove special
case around counting files in the qpdf corpus.

Also update to cmake variable rather than autoconf variable

With cmake, we are customizing the path for each test suite so we can
ensure we get the right qpdf without having to use an environment
variable.

Run compare images tests when QPDF_TEST_COMPARE_IMAGES is set rather
than when QPDF_SKIP_TEST_COMPARE_IMAGES is not set.