samples: posix: gettimeofday: Add sample.yaml

To make sure this sample is built in CI.

Also includes fixing prototype of main() to make it build without
warnings (which would be errors in CI).

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>

samples/posix/gettimeofday/sample.yaml

@@ -0,0 +1,12 @@
+sample:
+  description: POSIX API gettimeofday() example (with SNTP)
+  name: gettimeofday
+common:
+  filter: TOOLCHAIN_HAS_NEWLIB == 1
+  harness: net
+  min_ram: 32
+  min_flash: 96
+  tags: posix net
+tests:
+  sample.posix.gettimeofday:
+    harness: net

samples/posix/gettimeofday/src/main.c

@@ -10,7 +10,7 @@
 #include <sys/time.h>
 #include <unistd.h>
 
-void main(void)
+int main(void)
 {
 	struct timeval tv;