pcem: select Voodoo codegen by host capability

pcem: select Voodoo codegen by host capability

The imported Voodoo code only enabled its x86 code generators through
Windows-oriented preprocessor checks. That left Unix x86 builds with
the recompiler disabled even when the matching generator was compiled.

Derive explicit PCEM_VOODOO_CODEGEN macros from the host CPU and use
those macros for init, close, rendering, and the default recompiler
configuration.