Keep the colleague's microbu-esp32c5 tree in this repository

obu-firmware builds against vanetza-idf from microbu-esp32c5/external, but
that tree was gitignored, so a clone of this repository could not build the
firmware it ships. It is now committed here as ordinary files in its own
folder, microbu-esp32c5/: the colleague's commit cf4b99f plus the V2X2MAP
bridge's signature verification (--trust) used on the bench. Nothing is
fetched from or pushed to the colleague's repository; this repository and
its remotes carry everything. The folder's own .gitignore keeps build output,
downloaded components and private key material out, as it did there; the
committed file set is identical to that repository's tracked files.

The ESP32-C5 is still flashed from obu-firmware/, which only takes
vanetza-idf from microbu-esp32c5/, so the two stay separate folders.
FLASHING.md says how to take a newer version of the colleague's tree (copy
it over the folder, rebuild, test, commit).

microbu-esp32c5/external/vanetza-idf/vanetza/asn1/support/constraints.c

@@ -0,0 +1,94 @@
+#include "asn_internal.h"
+#include "constraints.h"
+
+int
+asn_generic_no_constraint(const asn_TYPE_descriptor_t *type_descriptor,
+                          const void *struct_ptr,
+                          asn_app_constraint_failed_f *cb, void *key) {
+    (void)type_descriptor;	/* Unused argument */
+	(void)struct_ptr;	/* Unused argument */
+	(void)cb;	/* Unused argument */
+	(void)key;	/* Unused argument */
+
+	/* Nothing to check */
+	return 0;
+}
+
+int
+asn_generic_unknown_constraint(const asn_TYPE_descriptor_t *type_descriptor,
+                               const void *struct_ptr,
+                               asn_app_constraint_failed_f *cb, void *key) {
+    (void)type_descriptor;	/* Unused argument */
+	(void)struct_ptr;	/* Unused argument */
+	(void)cb;	/* Unused argument */
+	(void)key;	/* Unused argument */
+
+	/* Unknown how to check */
+	return 0;
+}
+
+struct errbufDesc {
+    const asn_TYPE_descriptor_t *failed_type;
+    const void *failed_struct_ptr;
+	char *errbuf;
+	size_t errlen;
+};
+
+static void
+CC_PRINTFLIKE(4, 5)
+_asn_i_ctfailcb(void *key, const asn_TYPE_descriptor_t *td, const void *sptr,
+                const char *fmt, ...) {
+    struct errbufDesc *arg = key;
+	va_list ap;
+	ssize_t vlen;
+	ssize_t maxlen;
+
+	arg->failed_type = td;
+	arg->failed_struct_ptr = sptr;
+
+	maxlen = arg->errlen;
+	if(maxlen <= 0)
+		return;
+
+	va_start(ap, fmt);
+	vlen = vsnprintf(arg->errbuf, maxlen, fmt, ap);
+	va_end(ap);
+	if(vlen >= maxlen) {
+		arg->errbuf[maxlen-1] = '\0';	/* Ensuring libc correctness */
+		arg->errlen = maxlen - 1;	/* Not counting termination */
+		return;
+	} else if(vlen >= 0) {
+		arg->errbuf[vlen] = '\0';	/* Ensuring libc correctness */
+		arg->errlen = vlen;		/* Not counting termination */
+	} else {
+		/*
+		 * The libc on this system is broken.
+		 */
+		vlen = sizeof("<broken vsnprintf>") - 1;
+		maxlen--;
+		arg->errlen = vlen < maxlen ? vlen : maxlen;
+		memcpy(arg->errbuf, "<broken vsnprintf>", arg->errlen);
+		arg->errbuf[arg->errlen] = 0;
+	}
+
+	return;
+}
+
+int
+asn_check_constraints(const asn_TYPE_descriptor_t *type_descriptor,
+                      const void *struct_ptr, char *errbuf, size_t *errlen) {
+    struct errbufDesc arg;
+    int ret;
+
+    arg.failed_type = 0;
+    arg.failed_struct_ptr = 0;
+    arg.errbuf = errbuf;
+    arg.errlen = errlen ? *errlen : 0;
+
+    ret = type_descriptor->encoding_constraints.general_constraints(
+        type_descriptor, struct_ptr, _asn_i_ctfailcb, &arg);
+    if(ret == -1 && errlen) *errlen = arg.errlen;
+
+    return ret;
+}
+