www/lagrange: fix build on armv7, touch up
- unbundle devel/stb; this fixes the build on armv7
- define option SSE41 only on x86 platforms
Approved by: lcook (maintainer timeout)
PR: 283773
MFH: 2025Q1
(cherry picked from commit c48a3954186d2bcc77aef1586533227c9252dd28)