cppregex.cpp: move NetHack includes below c++ includes

Avoid a conflict with c++ std header file on at least one platform.

Build log prior:
In file included from DKA100:[DEVEL.nethack-37.sys.share]cppregex.cpp;1:12:
In file included from /SYS$COMMON/VSICXX$LIB/INCLUDE/LIB_CXX/INCLUDE/regex:768:
In file included from /SYS$COMMON/VSICXX$LIB/INCLUDE/LIB_CXX/INCLUDE/stdexcept:5
1:
In file included from /SYS$COMMON/VSICXX$LIB/INCLUDE/LIB_CXX/INCLUDE/exception:8
7:
In file included from /SYS$COMMON/VSICXX$LIB/INCLUDE/LIB_CXX/INCLUDE/cstdlib:91:
In file included from /SYS$COMMON/VSICXX$LIB/INCLUDE/LIB_CXX/INCLUDE/stdlib.h:10
3:
/SYS$COMMON/VSICXX$LIB/INCLUDE/DECC$RTLDEF/stdlib.h:200:24: error: too many argu
ments provided to function-like macro invocation
    void     abort    (void);
                       ^
../INCLUDE/vmsconf.h:307:9: note: macro 'abort' defined here
#define abort() vms_abort()             /* vmsmisc.c */
        ^

sys/share/cppregex.cpp

@@ -3,15 +3,16 @@
 /* Copyright (c) Sean Hunt  2015.                                 */
 /* NetHack may be freely redistributed.  See license for details. */
 
+#include <regex>
+#include <memory>
+#include <cstring>
+
 extern "C" {
 #include "config.h"
 #define CPPREGEX_C
 #include "extern.h"
 } // extern "C"
 
-#include <regex>
-#include <memory>
-#include <cstring>
 
 extern "C" { // rest of file