This allows PHPC to defer entirely to libmongoc for cross-option URI validation
Bump libmongoc to 1.21-dev
Build changes are ported from upstream CMake changes (see: CDRIVER-4249)
Per src/libmongoc/doc/installing.rst, the VERSION_CURRENT and VERSION_RELEASED files must now be generated. This requires Python and the GitPython pip module to run src/libmongoc/build/calc_release_version.py. A new libmongoc-version-current Makefile target has been added.
The AC_CHECK_FUNC macro has only the following form:
AC_CHECK_FUNC(function, [action-if-found], [action-if-not-found])
In most cases adding more arguments to macro call don't cause errors,
but it also doesn't have any functionality either.
The output path for this file was left incorrect in the previous PR for PHPC-1174, but the file isn't actually even used anymore per mongodb/mongo-c-driver@abc882dec9 (CDRIVER-2473).
GitHub's file finder filters out "build/" directories, among others, which can make it difficult to quickly access these files. Also, the "build/" directory doesn't provide much value here, since it only contains "autotools/".
