Add sys_hello and testbin/hellotest

`sys_hello` is a new syscall that just prints some text in the terminal.

`testbin/hellotest` is a userland binary that just calls `sys_hello`

userland/include/unistd.h

@@ -156,4 +156,6 @@ int execvp(const char *prog, char *const *args); /* calls execv */
 char *getcwd(char *buf, size_t buflen);          /* calls __getcwd */
 time_t time(time_t *seconds);                    /* calls __time */
 
+int hello(void);
+
 #endif /* _UNISTD_H_ */

userland/testbin/Makefile

@@ -7,7 +7,7 @@ TOP=../..
 
 SUBDIRS=add argtest badcall bigexec bigfile bigfork bigseek bloat conman \
 	crash ctest dirconc dirseek dirtest f_test factorial farm faulter \
-	filetest forkbomb forktest frack hash hog huge \
+	filetest forkbomb forktest frack hash hellotest hog huge \
 	malloctest matmult multiexec palin parallelvm poisondisk psort \
 	randcall redirect rmdirtest rmtest \
 	sbrktest schedpong sort sparsefile tail tictac triplehuge \

userland/testbin/hellotest/Makefile

@@ -0,0 +1,11 @@
+# Makefile for hello
+
+TOP=../../..
+.include "$(TOP)/mk/os161.config.mk"
+
+PROG=hellotest
+SRCS=hello.c
+BINDIR=/testbin
+
+.include "$(TOP)/mk/os161.prog.mk"
+

userland/testbin/hellotest/hello.c

@@ -0,0 +1,8 @@
+#include <unistd.h>
+
+extern int hello(void);
+
+int main() {
+  hello();
+  return 0;
+}