false positive cl compiler warnings

[Dave Love]

The compiler in the development sources emits warnings like:

Warning: Function `caaar' from cl package called at runtime

but caaar & al have compiler macros which make them safe to call.

I guess this means that the test for cl stuff is done in the wrong
place, but I've forgotten how it all works.  If it isn't possible to
DTRT in bytecomp.el, perhaps cl could add an extra symbol property for
safe functions, which could be checked to see if a compiler macro
expands safely.