It seems to have been an order of dependency issue. Works fine now.
jrs@laptop:~/sb/sb22/test$ cat sbc.sb
PRINT "Script BASIC\n"
jrs@laptop:~/sb/sb22/test$ gcc -Os sbc.c -I/home/jrs/sb/source /usr/lib/sb.a -ldl -lm -lpthread -lscriba -o sbc
jrs@laptop:~/sb/sb22/test$ ./sbc
Script BASIC
jrs@laptop:~/sb/sb22/test$ ls -l sbc
-rwxrwxr-x 1 jrs jrs 24655 Apr 15 14:20 sbc
jrs@laptop:~/sb/sb22/test$ file sbc
sbc: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.24, BuildID[sha1]=a8ae87e049b81b42c037ae74bd21ad925b4cb0a0, not stripped
jrs@laptop:~/sb/sb22/test$ strip -s sbc
jrs@laptop:~/sb/sb22/test$ ls -l sbc
-rwxrwxr-x 1 jrs jrs 19992 Apr 15 14:43 sbc
jrs@laptop:~/sb/sb22/test$