add sys_printchar

userland/testbin/printchartest/printchartest.c

@@ -0,0 +1,17 @@
+#include <unistd.h>
+
+extern int printchar(char c);
+
+int main() {
+
+  printchar('C');
+  printchar('S');
+  printchar('E');
+  printchar('4');
+  printchar('0');
+  printchar('0');
+  printchar('1');
+  printchar('\n');
+
+  return 0;
+}