Fix RUBY_FFI-17 by including a version of roundup() if it is not already defined.
Fix RUBY_FFI-17 by including a version of roundup() if it is not already defined.

Patch from coneill.

ffi/ffi,sparkchaser/ffi,ffi/ffi,MikaelSmith/ffi,majioa/ffi,yghannam/ffi,MikaelSmith/ffi,yghannam/ffi,majioa/ffi,majioa/ffi,ferventcoder/ffi,MikaelSmith/ffi,ffi/ffi,sparkchaser/ffi,yghannam/ffi,ferventcoder/ffi,mvz/ffi,tduehr/ffi,yghannam/ffi,yghannam/ffi,tduehr/ffi,majioa/ffi,sparkchaser/ffi,MikaelSmith/ffi,ferventcoder/ffi,tduehr/ffi,mvz/ffi,mvz/ffi,ferventcoder/ffi,sparkchaser/ffi,mvz/ffi,tduehr/ffi