Some fixes and additions

[kaechele]

• remove fann BR, deprecated in favor of torch
• add gd support
• remove gmime BR, it's unused
• add libcurl, enables the use of UCL URL includes
• add openblas support for enhanced regex performance
• switch to pcre2 for enhanced regex performance
• drop some unused defines in the cmake call

[kaechele]

Some background:

Since Rspamd 1.7, libfann module is deprecated in honor of Lua Torch.

https://rspamd.com/doc/modules/neural.html

but that looks like it's going to change with the next release again: https://github.com/rspamd/rspamd/issues/2942

[LorbusChris]

this is awesome, thank you very much!