LMDB Support for driver flags

[Girgias]

This fixes #8856

I'm not exactly sure about the implementation for the driver flags as the way DBA is currently built the headers seem to be added somewhat magically.

These commit should also be kept separately.

[cmb69]

Thank you for the PR! However, I don't like to introduce DBA_LMDB_USE_SUB_DIR; after all, this is a flags parameter, and as such a bitmask. Passing 0 should be sufficient, shouldn't it?

[Girgias]

I think the reason why I added the constant is that the default would not be 0 and it feels a bit weird, but I can remove it

[cmb69]

Yeah, I see your point. It is unfortunate, that we started with MDB_NOSUBDIR as default. Maybe keep DBA_LMDB_USE_SUB_DIR.

[Girgias]

@kocsismate why am I getting an:

In ./ext/dba/dba.stub.php:
Constant DBA_LMDB_NO_SUB_DIR must have a @cvalue annotation

Error? I don't understand why it needs a CVALUE annotation as the value is defined in the stubs?

[kocsismate]

why am I getting an:
In ./ext/dba/dba.stub.php:
Constant DBA_LMDB_NO_SUB_DIR must have a @cvalue annotation
Error? I don't understand why it needs a CVALUE annotation as the value is defined in the stubs?

But the value is UNKNOWN, right? UNKNOWN value means that REGISTER_*_CONSTANT() calls should use the C constant as value. If there is a proper constant value but there's no @cvalue then the former is used. If there are both, then the C constant value is used in C code, and an assertion is added that the 2 values match.

[Girgias]

why am I getting an:
In ./ext/dba/dba.stub.php:
Constant DBA_LMDB_NO_SUB_DIR must have a @cvalue annotation
Error? I don't understand why it needs a CVALUE annotation as the value is defined in the stubs?

But the value is UNKNOWN, right? UNKNOWN value means that REGISTER_*_CONSTANT() calls should use the C constant as value. If there is a proper constant value but there's no @cvalue then the former is used. If there are both, then the C constant value is used in C code, and an assertion is added that the 2 values match.

The value is not UNKNOWN it is 0 as it's a constant I created which does not have an equivalent in C, which is why I'm confused by the error

[cmb69]

Looks good to me (besides the two nits). Please add a note in NEWS and UPGRADING when merging.