[analyzer] Cache whether a function is generally inlineable.

Certain properties of a function can determine ahead of time whether or not
the function is inlineable, such as its kind, its signature, or its
location. We can cache this value in the FunctionSummaries map to avoid
rechecking these static properties for every call.

Note that the analyzer may still decide not to inline a specific call to
a function because of the particular dynamic properties of the call along
the current path.

No intended functionality change.

llvm-svn: 178515