legacy junk compatibility grab-bag

- add the rest of the junk traditionally in sys/param.h
- add prototypes for some nonstandard functions
- add _GNU_SOURCE to their source files so the compiler can check proto

src/linux/daemon.c

@@ -1,3 +1,4 @@
+#define _GNU_SOURCE
 #include <fcntl.h>
 #include <unistd.h>
 

src/termios/cfmakeraw.c

@@ -1,3 +1,4 @@
+#define _GNU_SOURCE
 #include <termios.h>
 
 void cfmakeraw(struct termios *t)