CVE-2023-28320: siglongjmp race condition

Summary: If the system has no POSIX or Windows threading support, `USE_ALARM_TIMEOUT` codepath will be used in `lib/hostip.c`. If two threads will perform DNS resolving, a wrong register context can be used on the signal handler`siglongjmp` call if DNS timeout occurs. Typically this results in …

diff --git a/lib/hostip.c b/lib/hostip.c
index 2381290fd..0148f2861 100644
--- a/lib/hostip.c
+++ b/lib/hostip.c
@@ -75,6 +75,7 @@
 /* alarm-based timeouts can only be used with all the dependencies satisfied */
 #define USE_ALARM_TIMEOUT
 #endif
+#define USE_ALARM_TIMEOUT

 #define …