linux: update comm field in uv_set_process_title()

Makes the new process name visible in both `ps` and `ps a`, with the caveat
that `ps` will only print the first 16 characters.

Before this commit, `ps` kept reporting the old process name.

src/unix/linux/linux-core.c

@@ -30,6 +30,7 @@
 
 #include <net/if.h>
 #include <sys/param.h>
+#include <sys/prctl.h>
 #include <sys/sysinfo.h>
 #include <unistd.h>
 #include <fcntl.h>
@@ -167,6 +168,10 @@ uv_err_t uv_set_process_title(const char* title) {
   if (process_title.len)
     strncpy(process_title.str, title, process_title.len - 1);
 
+#if defined(PR_SET_NAME)
+  prctl(PR_SET_NAME, title);
+#endif
+
   return uv_ok_;
 }