util: add eregcomp: show descriptive error message on regcomp error

util/eregcomp.c

@@ -0,0 +1,25 @@
+#include <regex.h>
+#include <stdio.h>
+#include <sys/types.h>
+
+#include "../util.h"
+
+int
+enregcomp(int status, regex_t *preg, const char *regex, int cflags)
+{
+    char errbuf[BUFSIZ] = "";
+    int r;
+
+    if((r = regcomp(preg, regex, cflags)) == 0)
+        return r;
+
+    regerror(r, preg, errbuf, sizeof(errbuf));
+    enprintf(status, "invalid regex: %s\n", errbuf);
+    return r;
+}
+
+int
+eregcomp(regex_t *preg, const char *regex, int cflags)
+{
+	return enregcomp(1, preg, regex, cflags);
+}