Fix SONAME to include the ABI version suffix

[austek]

Fixes #1.

Summary

The shared library's embedded SONAME was passed as -Wl,$(SONAME)$(LIB_NAME) — e.g. plain libsonic.so — while the file actually built and installed is libsonic.so.0.3.0, with libsonic.so.0 as the versioned runtime symlink pointing at it, exactly as reported:

```
$ readelf -aW /usr/lib64/libsonic.so.0 | grep -i SONAME
0x000000000000000e (SONAME) Library soname: [libsonic.so]
```

A correct SONAME must match that runtime symlink (libsonic.so.0), not the unversioned dev symlink (libsonic.so) used only at link time — a mismatched SONAME breaks the usual shared-library upgrade path, since the dynamic linker embeds and looks up the SONAME, not the on-disk filename.

Adds SONAME_SUFFIX (.0, following the LIB_TAG platform-conditional pattern already in this file) rather than changing LIB_NAME itself, since LIB_NAME is also used unversioned elsewhere (the dev symlink, install rules). Empty on Darwin, where SONAME is actually an install_name that already matches the unversioned libsonic.dylib file this Makefile builds there (LIB_TAG is empty on Darwin too) — so Darwin's behavior is unchanged.

Also filed and fixed upstream: waywardgeek/sonic#70 — this repo forked from there and has the identical unqualified -Wl,$(SONAME)$(LIB_NAME) lines.

Test plan

• readelf -d libsonic.so.0.3.0 | grep -i soname — now libsonic.so.0 (was libsonic.so), matching the reporter's exact repro command
• readelf -d libsonic_internal.so.0.3.0 | grep -i soname — now libsonic_internal.so.0
• Full make — succeeds, symlinks (libsonic.so, libsonic.so.0 → libsonic.so.0.3.0) unchanged