gnu: blis: Update to 0.8.1.

gnu: blis: Update to 0.8.1.

* gnu/packages/maths.scm (make-blis): Remove internal function.
Inline into ...
(bliss): ... this variable. Update to 0.8.1.
[native-inputs]: Add "python" and "perl".
[arguments]: Adjust 'configure' phase to take advantage of new support
for "configuration families" with runtime hardware detection. Select
configuration automatically based on target systems, and allow
"--blis-config=" in #:configure-flags to override the default.
When building for x86_64, include all supported microarchetecture
specializations. Add "--enable-verbose-make" configure flag for better
build logs. Stop ignoring other flags from #:configure-flags.
Remove explicit #:substitutable? argument: the package is now always
substitutable. Add (srfi srfi-1) to #:modules.
(blis/x86_64): Remove internal macro.
(blis-sandybridge): Remove package: included in 'blis'.
(blis-haswell): Remove package: included in 'blis'.
(blis-knl): Remove package: included in 'blis'.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>