deps: update cpufeatures to e8178f9 (blacklist SSBS)

Picks up gbaraldi/cpufeatures#5 which blacklists FEAT_SSBS from
hw_feature_mask. SSBS is a speculative execution mitigation that
doesn't affect codegen but was inconsistently present across LLVM
CPU definitions (apple-a16 has it, apple-m4 doesn't), causing
false target mismatches on Apple Silicon.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: gbaraldi

deps/cpufeatures.version

@@ -3,5 +3,5 @@
 ## source build
 CPUFEATURES_VER := 0.2.0
 CPUFEATURES_GIT_URL := https://github.com/gbaraldi/cpufeatures.git
-CPUFEATURES_TAR_URL := https://github.com/gbaraldi/cpufeatures/archive/8bdf629fb6baef0126e23d737d46010085342cf6.tar.gz
-CPUFEATURES_SHA := 8bdf629fb6baef0126e23d737d46010085342cf6
+CPUFEATURES_TAR_URL := https://github.com/gbaraldi/cpufeatures/archive/e8178f952870a83c506f3f08150e3915193ab862.tar.gz
+CPUFEATURES_SHA := e8178f952870a83c506f3f08150e3915193ab862