On Windows, the cli and phpdbg SAPIs have variants (cli-win32 and
phpdbgs, respectively) which are build by default. However, the
variants share some files, what leads to duplicate build rules in the
generated Makefile. NMake throws warning U4004[1], but proceeds
happily, ignoring the second build rule. That means that different
flags for duplicate rules are ignored, hinting at a potential problem.
We solve this by introducing an additional (optional) argument to
`SAPI()` and `ADD_SOURCES()` which can be used to avoid such duplicate
build rules. It's left to the SAPI maintainers to make sure that
appropriate rules are created. We fix this for phpdbgs right away,
which currently couldn't be build without phpdbg due to the missing
define; we remove the unused `PHP_PHPDBG_EXPORTS` flag altogether.
[1] <https://learn.microsoft.com/en-us/cpp/error-messages/tool-errors/nmake-warning-u4004>
Closes GH-17545.
3955b01653