audio/spiralsynthmodular: Fix "undefined symbol" errors at runtime

• Behavior *
• At runtime, for each synth plugin, we got:

dlerror() output:
/usr/local/lib/SpiralPlugins/AmpPlugin.so: Undefined symbol "_ZN10SpiralInfo6LOCALEE"

• Why *
• It seems this comes from the way newer compiler manage static properties. (SSM is 25yo).
• This error has already been reported long times ago on Linux distro.

• Fix *
• A way to fix it without rewriting the wheel is to inline static properties in the header.

While here improve port:

• Add LICENSE.
• Register dependiencies.
• Replace CPPFLAGS and LIBS with USES=localbase.
• Parametrize version in WRKSRC.
• Remove unnecessary REINPLACE_CMD in SpiralSound/Plugins/LADSPAPlugin/Makefile.in.
• Merge STRIP_CMD.

PR: 293552
MFH: 2026Q1
(cherry picked from commit 8fedf8cd90ccc775af0f5e2a203f4c94f233bdd1)