COMPATIBLE_INTERFACE_STRING
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Properties which must be string-compatible with their link interface

The COMPATIBLE_INTERFACE_STRING property may contain a list of
properties for this target which must be the same when evaluated as a
string in the INTERFACE of all linked dependees.  For example, if a
property "FOO" appears in the list, then for each dependee, the
"INTERFACE_FOO" property content in all of its dependencies must be
equal with each other, and with the "FOO" property in the dependee.
If the property is not set, then it is ignored.  Note that for each
dependee, the set of properties from this property must not intersect
with the set of properties from the COMPATIBLE_INTERFACE_BOOL
property.
