Compiling extension C with MingW in windows, Error...

Hi, I am tryng to compile a C extension in windows using Minigw but always I get the same error

C:\Program Files\PostgreSQL\8.3\share\exte_c>C:\mingw\bin\gcc -shared -o pg2.dll
 pg2.o
pg2.o:pg2.c:(.text+0x86): undefined reference to `_imp__CurrentMemoryContext'
pg2.o:pg2.c:(.text+0x92): undefined reference to `MemoryContextAlloc'
collect2: ld returned 1 exit status

This error is just when it links.

Aparently this occur just when use text vardata

This is the code for my function. This function was taken from manual page but it doesnt work neither.

#include <string.h>
#include "fmgr.h"

#ifdef PG_MODULE_MAGIC
PG_MODULE_MAGIC;
#endif


PG_FUNCTION_INFO_V1(concat_text);

Datum
concat_text(PG_FUNCTION_ARGS)
{
    text  *arg1 = PG_GETARG_TEXT_P(0);
    text  *arg2 = PG_GETARG_TEXT_P(1);
    int32 new_text_size = VARSIZE(arg1) + VARSIZE(arg2) - VARHDRSZ;
   
    text *new_text = (text *) palloc(new_text_size);

    VARATT_SIZEP(new_text) = new_text_size;
   //
    memcpy(VARDATA(new_text), VARDATA(arg1), VARSIZE(arg1)-VARHDRSZ);
    memcpy(VARDATA(new_text) + (VARSIZE(arg1)-VARHDRSZ),
   //
   VARDATA(arg2), VARSIZE(arg2)-VARHDRSZ);
    PG_RETURN_TEXT_P(new_text);
}

Any clues about this ???

*-------------------------------------------------------*
*-Edwin Quijada
*-Developer DataBase
*-JQ Microsistemas
*-Soporte PostgreSQL
*-www.jqmicrosistemas.com
*-809-849-8087
*-------------------------------------------------------*