www/librewolf: Fix build on i386, improve port

• Fix build on i386 - use www/node24 on i386 and hande sse2.
• Unification of Makefile with Firefox - make it more similar.
• Use ${DESKTOPDIR} instead if ${PREFIX}/share/applications.

PR: 288107
MFH: 2025Q3
(cherry picked from commit 6f3a8ff37218c5200c8822de90577e95811c3a5e)