Make all scripts produce .S, make interpretation of $(CFLAGS)
pre-processor's responsibility, start accepting $(PERLASM_SCHEME).
[$(PERLASM_SCHEME) is redundant in this case, because there are
no deviataions between Solaris and Linux assemblers. This is
purely to unify .pl->.S handling across all targets.]

Reviewed-by: Richard Levitte <levitte@openssl.org>