Recognize self calls during xc.

DEFUN needs to expand into NAMED-LAMBDA, and IR1-CONVERT-LAMBDALIKE
shouldn't recognize calls to functions with transforms or templates as
self calls, otherwise (defun car (x) (car x)) breaks.
Simplify WALK-METHOD-LAMBDA and consumers thereof.

The earliest PCL releases had many different ways to expose CALL-NEXT-METHOD
(named ADD-LEXICAL-FUNCTIONS-TO-OPTIMIZED-n for n=1..6) depending on whether
it was ever an operand to FUNCTION in a particular method and/or whether the
method always, sometimes, or never passed arguments to CALL-NEXT-METHOD.
(And a local macro binding was generally favored over a local function)
In contrast, the 'closurep' flag served no purpose in SBCL, and by providing
NEXT-METHOD-P gratuitously, there is no need to pre-scan for uses of it.
Avoid putting two safepoints in a row when doing self calls.

Because it's a loop it needs a safepoint, but there's already one at
the beginning of a function.
Restore exception handling on Windows-x86.

GCC decided to change its default stack alignment to 16 bytes, and now
we depend on aligning SAPs on the stack, the exception_handler_wrapper
assembly wrapper didn't maintain 16-byte stack alignment causing
problems. Fixing exception_handler_wrapper would be easy, but SBCL
only observes 4-byte alignment on x86oids, so it's better to convince
GCC with -mpreferred-stack-boundary=2 (and wait until we have the same
problem on Linux).
Restore effectiveness of *FGENS* cache (as mentioned on sbcl-devel)