MDEV-28884: include kernel information in crashing signal handler

Recent adventures in liburing and btrfs have shown up some kernel
version dependent bugs. Having a bug report of accurace kernel version
can start to correlate these errors sooner.

On Linux, /proc/version contains the kernel version.

FreeBSD has kern.version (per man 8 sysctl), so include that too.

Example output:

Max nice priority         0                    0
Max realtime priority     0                    0
Max realtime timeout      unlimited            unlimited            us
Core pattern: |/usr/lib/systemd/systemd-coredump %P %u %g %s %t %c %h

Kernel version: Linux version 5.19.0-0.rc2.21.fc37.x86_64 (mockbuild@bkernel01.iad2.fedoraproject.org) (gcc (GCC) 12.1.1 20220507 (Red Hat 12.1.1-1), GNU ld version 2.38-14.fc37) #1 SMP PREEMPT_DYNAMIC Mon Jun 13 15:27:24 UTC 2022

Segmentation fault (core dumped)

sql/signal_handler.cc

@@ -81,6 +81,12 @@ static inline void output_core_info()
     my_safe_printf_stderr("Core pattern: %.*s\n", (int) len, buff);
     my_close(fd, MYF(0));
   }
+  if ((fd= my_open("/proc/version", O_RDONLY, MYF(0))) >= 0)
+  {
+    len= my_read(fd, (uchar*)buff, sizeof(buff),  MYF(0));
+    my_safe_printf_stderr("Kernel version: %.*s\n", (int) len, buff);
+    my_close(fd, MYF(0));
+  }
 #endif
 #elif defined(__APPLE__) || defined(__FreeBSD__)
   char buff[PATH_MAX];
@@ -89,6 +95,10 @@ static inline void output_core_info()
   {
     my_safe_printf_stderr("Core pattern: %.*s\n", (int) len, buff);
   }
+  if (sysctlbyname("kern.version", buff, &len, NULL, 0) == 0)
+  {
+    my_safe_printf_stderr("Kernel version: %.*s\n", (int) len, buff);
+  }
 #else
   char buff[80];
   my_getwd(buff, sizeof(buff), 0);