Add hello world to baremetal tests

tests/Makefile

@@ -6,7 +6,8 @@ LDFLAGS= -static
 include libgloss.mk
 
 PROGRAMS = pwm blkdev accum charcount nic-loopback big-blkdev pingd \
-           streaming-passthrough streaming-fir nvdla spiflashread spiflashwrite fft gcd
+           streaming-passthrough streaming-fir nvdla spiflashread spiflashwrite fft gcd \
+           hello
 
 spiflash.img: spiflash.py
 	python3 $<

tests/hello.c

@@ -0,0 +1,6 @@
+#include <stdio.h>
+
+int main(void) {
+  printf("Hello world\n");
+  return 0;
+}