#-sb-xc (progn ...) considered harmful in SBCL sources

[Tobias C. Rittweiler]

M-. on sb-c::defknown brings you to the definition of DEFTRANFORM, so
a off-by-one.

This comes from the #-sb-xc (progn ...) a few forms above which is not
taken into account while compiler/macros.lisp is compiled itself, but will
be taken account when Slime's re-reads the source.

So the idiom #-sb-xc (progn ...) as a toplevel form must be considered
harmful, and (progn #-sb-xc (progn ...)) should be used instead, or
something similiar.

This should probably be guarded against by some source-grovelling script.
(I think there is one already to guard against whitespacification.)