The conditional inclusion of either the library or the header-only
version of the Boost.Test header wasn't tremendously useful in practice
because the tests/CMakeLists.txt file would unconditionally add compile
definitions to basically fore dynamic linking.
This patch adds feature detection to the tests/CMakeLists.txt file to
determine whether to use dynamic linking, static linking or the
header-only version (in that order of preference, for best performance).
The automatic detection could be overridden if needed by defining the
TOML11_WITH_BOOST_TEST_{HEADER,STATIC,DYNAMIC}
variables on the CMake command line.
While we are at it, instead of having a conditional
#define BOOST_TEST_NO_LIB
in each unit test file, handle this once in the CMakeLists.txt file.
Most unit test files checked UNITTEST_FRAMEWORK_LIBRARY_EXIST and
adapted themselves accordingly to either use the header-only version or
link with the library. Alas, eight files didn't so the project couldn't
really be tested with the header-only version of that Boost library.
This patch adds the missing pre-processor logic to the files that were
missing it. The style of using no indentation after the '#' was
followed from the existing unit test files. Some other files in this
repository do indent their pre-processor logic, though.
Since replicating the conditional in every file is kind of verbose,
tedious and, apparently, easily forgotten, I'm wondering whether
isolating that logic into a tiny little auxiliary header and then
unconditionally including that one in each unit test file would be a
good idea, though.
