vasprintf is called like:

 int asprintf(char **ptr, const char *format, ...)
{
	va_list ap;
	int ret;
	
	*ptr = NULL;
	va_start(ap, format);
	ret = vasprintf(ptr, format, ap);
	va_end(ap);

	return ret;
}

 int vasprintf(char **ptr, const char *format, va_list ap)
{
	int ret;
	va_list ap2;

	VA_COPY(ap2, ap);
	
	ret = vsnprintf(NULL, 0, format, ap2);
	if (ret <= 0) return ret;
        +va_end (ap2);

	(*ptr) = (char *)malloc(ret+1);
	if (!*ptr) return -1;

        +va_start (ap2, format);
	VA_COPY(ap2, ap);

	ret = vsnprintf(*ptr, ret+1, format, ap2);
        +va_end (ap2);

	return ret;
}

Produces on s390 (without modifications), works on x86:

 gcc -c -Wall -g -O2  -DHAVE_SNPRINTF -DHAVE_PIPE -DHAVE_STPCPY -D_GNU_SOURCE=1 -o snprintf.o snprintf.c
 snprintf.c: In function 'vasprintf':
 snprintf.c:856: error: incompatible types in assignment
 snprintf.c:864: error: incompatible types in assignment

Produces on x86 (with modifications):
 gcc -c -Wall -g -O2  -DHAVE_SNPRINTF -DHAVE_PIPE -DHAVE_STPCPY -D_GNU_SOURCE=1 -o snprintf.o  snprintf.c
 snprintf.c: In function ‘vasprintf’:
 snprintf.c:865: error: ‘va_start’ used in function with fixed args