winecrt0: Add a fallback implementation of __wine_dbg_strdup().

dlls/winecrt0/Makefile.in

 MODULE    = libwinecrt0.a
 
 C_SRCS = \
+	debug.c \
 	delay_load.c \
 	dll_entry.c \
 	dll_main.c \

dlls/winecrt0/debug.c

+/*
+ * Fallbacks for debugging functions when running on Windows
+ *
+ * Copyright 2019 Alexandre Julliard
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
+ */
+
+#ifdef _WIN32
+
+#include "config.h"
+#include "wine/port.h"
+
+#include "windef.h"
+#include "winbase.h"
+#include "wine/debug.h"
+
+static const char * (__cdecl *p__wine_dbg_strdup)( const char *str );
+
+static void load_func( void **func, const char *name, void *def )
+{
+    if (!*func)
+    {
+        HMODULE module = GetModuleHandleA( "ntdll.dll" );
+        void *proc = GetProcAddress( module, name );
+        interlocked_xchg_ptr( func, proc ? proc : def );
+    }
+}
+#define LOAD_FUNC(name) load_func( (void **)&p ## name, #name, fallback ## name )
+
+/* FIXME: this is not 100% thread-safe */
+static const char * __cdecl fallback__wine_dbg_strdup( const char *str )
+{
+    static char *list[32];
+    static int pos;
+    char *ret = _strdup( str );
+    int idx;
+
+    idx = interlocked_xchg_add( &pos, 1 ) % ARRAY_SIZE(list);
+    free( interlocked_xchg_ptr( (void **)&list[idx], ret ));
+    return ret;
+}
+
+const char * __cdecl __wine_dbg_strdup( const char *str )
+{
+    LOAD_FUNC( __wine_dbg_strdup );
+    return p__wine_dbg_strdup( str );
+}
+
+#endif  /* _WIN32 */