Build with debug symbols

This makes it possible to debug stuff:

    $ gdb ./scheme
    (gdb) b scheme_entry
    (gdb) run
    (gdb) list
    ...
    (gdb) info registers eax
    (gdb) s
    (gdb) info registers eax

scm/inc/Makefile

@@ -2,7 +2,7 @@ run-scheme: scheme
	./scheme
scheme: scheme.s driver.c
	gcc -O3 scheme.s driver.c -o $@
	gcc -O3 -g scheme.s driver.c -o $@
asm: scheme.s
	cat scheme.s