[CM] S7 questions and libc issue

[bil at ccrma.Stanford.EDU]

For gcc, use

   gcc -o s7 s7.c -I. -lm -DWITH_MAIN -DWITH_C_LOADER=0 -pthread -static

libc_s7.so gives FFI bindings for a large portion of libc.
repl.scm needs it to get raw terminal handlers. The
WITH_C_LOADER switch is what you needed, I think.