Implement a new system-based matching harness.

The intent is to look for platform-specific facilities for regex
matching, to provide portable MENUCOLORS configuration files.

This is a prototype implementation being committed to see if Windows can
use the POSIX regex implementation provided with the C++11 standard
library. If this works, I will write a harness for POSIX regexes and for
pmatch(), and those can be linked in by platforms as appropriate.

pmatch() should be used only as a very last resort, because it breaks
compatibility between platforms.

sys/share/cppregex.cpp

@@ -0,0 +1,51 @@
+/* NetHack 3.5  cppregex.cpp	$NHDT-Date$  $NHDT-Branch$:$NHDT-Revision$ */
+/* NetHack 3.5	cppregex.cpp	$Date: 2009/05/06 10:44:33 $  $Revision: 1.4 $ */
+/* Copyright (c) Sean Hunt  2015.                                 */
+/* NetHack may be freely redistributed.  See license for details. */
+
+#include <regex>
+#include <memory>
+
+extern "C" {
+  #include <nhregex.h>
+
+  struct nhregex {
+    std::unique_ptr<std::regex> re;
+    std::unique_ptr<std::regex_error> err;
+  };
+
+  struct nhregex *regex_init(void) {
+    return new nhregex;
+  }
+
+  boolean regex_compile(const char *s, struct nhregex *re) {
+    if (!re)
+      return FALSE;
+    try {
+      re->re.reset(new std::regex(s, std::regex::extended | std::regex::nosubs | std::regex::optimize));
+      re->err.reset(nullptr);
+      return TRUE;
+    } catch (const std::regex_error& err) {
+      re->err.reset(new std::regex_error(err));
+      re->re.reset(nullptr);
+      return FALSE;
+    }
+  }
+
+  const char *regex_error_desc(struct nhregex *re) {
+    if (re->err)
+      return re->err->what();
+    else
+      return nullptr;
+  }
+
+  boolean regex_match(const char *s, struct nhregex *re) {
+    if (!re->re)
+      return false;
+    return regex_search(s, *re->re, std::regex_constants::match_any);
+  }
+
+  void regex_free(struct nhregex *re) {
+    delete re;
+  }
+}