It looks like most of Intel processors and susceptible to this hardware vulnerability that lets you read protected memory at the user level. AMD is not vulnerable to Meltdown, but it is for Spectre in general. Meltdown is just one type of Spectre attack.
Fortunately for Mac OS 10.12.3 users, Apple has implemented a kernel page-table isolation (KPTI) to protect against Meltdown. Reportedly there are KPTI's available for Linux. I have not heard anything for Windows yet which seems to be vulnerable. If you host FMS on a Mac, upgrading to 10.12.3 is probably a good idea.
The biggest vulnerability seems to be Cloud servers like FileMaker's Cloud on Amazon and other AWS services.
Info on this is rapidly changing. Meltdown info at Wikipedia is at: Meltdown (security vulnerability) - Wikipedia