MINOR: sample: Add "quic_enabled" sample fetch

This sample fetch returns a boolean. True if the support for QUIC transport
protocol was built and if this protocol was not disabled by "no-quic"
global option.

Must be backported to 2.7.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index 9bd2627..5d62651 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -18846,6 +18846,14 @@
   possible action could be to reject new users but still accept old ones. See
   also the "avg_queue", "be_conn", and "be_sess_rate" fetches.
 
+quic_enabled : boolean
+  Warning: QUIC support in HAProxy is currently experimental. Configuration may
+  change without deprecation in the future.
+
+  Return true when the support for QUIC transport protocol was compiled and
+  if this procotol was not disabled by "no-quic" global option. See also "no-quic"
+  global option.
+
 rand([<range>]) : integer
   Returns a random integer value within a range of <range> possible values,
   starting at zero. If the range is not specified, it defaults to 2^32, which
diff --git a/src/sample.c b/src/sample.c
index 7a612fc..953e463 100644
--- a/src/sample.c
+++ b/src/sample.c
@@ -4393,6 +4393,19 @@
 	return 0;
 }
 
+/* Check if QUIC support was compiled and was not disabled by "no-quic" global option */
+static int smp_fetch_quic_enabled(const struct arg *args, struct sample *smp, const char *kw, void *private)
+{
+	smp->data.type = SMP_T_BOOL;
+	smp->flags = 0;
+#ifdef USE_QUIC
+	smp->data.u.sint = !(global.tune.options & GTUNE_NO_QUIC);
+#else
+	smp->data.u.sint = 0;
+#endif
+	return smp->data.u.sint;
+}
+
 /* Note: must not be declared <const> as its list will be overwritten.
  * Note: fetches that may return multiple types must be declared as the lowest
  * common denominator, the type that can be casted into all other ones. For
@@ -4407,6 +4420,7 @@
 	{ "hostname",     smp_fetch_hostname, 0,         NULL, SMP_T_STR,  SMP_USE_CONST },
 	{ "nbproc",       smp_fetch_nbproc,0,            NULL, SMP_T_SINT, SMP_USE_CONST },
 	{ "proc",         smp_fetch_proc,  0,            NULL, SMP_T_SINT, SMP_USE_CONST },
+	{ "quic_enabled", smp_fetch_quic_enabled, 0,     NULL, SMP_T_BOOL, SMP_USE_CONST },
 	{ "thread",       smp_fetch_thread,  0,          NULL, SMP_T_SINT, SMP_USE_CONST },
 	{ "rand",         smp_fetch_rand,  ARG1(0,SINT), NULL, SMP_T_SINT, SMP_USE_CONST },
 	{ "stopping",     smp_fetch_stopping, 0,         NULL, SMP_T_BOOL, SMP_USE_INTRN },