Why do I get a DisjunctionsNotSupportedException when doing a SOQL query on Custom Metadata?

Custom Metadata supports a limited SOQL syntax, and "OR" statements are not supported. From the documentation:

Custom metadata types support the following SOQL query syntax.

SELECT fieldList [...]
FROM objectType
    [USING SCOPE filterScope]
[WHERE conditionExpression]
[ORDER BY field {ASC|DESC} [NULLS {FIRST|LAST}] ]

• The fieldList can include only non-relationship fields.
• FROM can include only one object.
• You can’t use COUNT with custom metadata types.
• You can use the following operators.
  • IN and NOT IN
  • =, >, >=, <, <=, and !=
  • LIKE, including wild cards
  • AND
• You can use ORDER BY, ASC, and DESC with multiple fields.

Notice that "OR" is not supported. Apparently that's called a "Disjunction"