Workaround of GC crash on Cygwin64

Patch from <http://www.j10n.org/files/w3m-cvs-1.1055-win64gc.patch>,
[w3m-dev:04469] on 2013-10-14.

indep.c

@@ -707,6 +707,111 @@ shell_quote(char *str)
     return str;
 }
 
+void *
+xrealloc(void *ptr, size_t size)
+{
+    void *newptr = realloc(ptr, size);
+    if (newptr == NULL) {
+	fprintf(stderr, "Out of memory\n");
+	exit(-1);
+    }
+    return newptr;
+}
+
+/* Define this as a separate function in case the free() has
+ * an incompatible prototype. */
+void
+xfree(void *ptr)
+{
+    free(ptr);
+}
+
+void *
+w3m_GC_realloc_atomic(void *ptr, size_t size)
+{
+    return ptr ? GC_REALLOC(ptr, size) : GC_MALLOC_ATOMIC(size);
+}
+
+void
+w3m_GC_free(void *ptr)
+{
+    GC_FREE(ptr);
+}
+
+void
+growbuf_init(struct growbuf *gb)
+{
+    gb->ptr = NULL;
+    gb->length = 0;
+    gb->area_size = 0;
+    gb->realloc_proc = &w3m_GC_realloc_atomic;
+    gb->free_proc = &w3m_GC_free;
+}
+
+void
+growbuf_init_without_GC(struct growbuf *gb)
+{
+    gb->ptr = NULL;
+    gb->length = 0;
+    gb->area_size = 0;
+    gb->realloc_proc = &xrealloc;
+    gb->free_proc = &xfree;
+}
+
+void
+growbuf_clear(struct growbuf *gb)
+{
+    (*gb->free_proc) (gb->ptr);
+    gb->ptr = NULL;
+    gb->length = 0;
+    gb->area_size = 0;
+}
+
+Str
+growbuf_to_Str(struct growbuf *gb)
+{
+    Str s;
+
+    if (gb->free_proc == &w3m_GC_free) {
+	growbuf_reserve(gb, gb->length + 1);
+	gb->ptr[gb->length] = '\0';
+	s = New(struct _Str);
+	s->ptr = gb->ptr;
+	s->length = gb->length;
+	s->area_size = gb->area_size;
+    } else {
+	s = Strnew_charp_n(gb->ptr, gb->length);
+	(*gb->free_proc) (gb->ptr);
+    }
+    gb->ptr = NULL;
+    gb->length = 0;
+    gb->area_size = 0;
+    return s;
+}
+
+void
+growbuf_reserve(struct growbuf *gb, int leastarea)
+{
+    int newarea;
+
+    if (gb->area_size < leastarea) {
+	newarea = gb->area_size * 3 / 2;
+	if (newarea < leastarea)
+	    newarea = leastarea;
+	newarea += 16;
+	gb->ptr = (*gb->realloc_proc) (gb->ptr, newarea);
+	gb->area_size = newarea;
+    }
+}
+
+void
+growbuf_append(struct growbuf *gb, const char *src, int len)
+{
+    growbuf_reserve(gb, gb->length + len);
+    memcpy(&gb->ptr[gb->length], src, len);
+    gb->length += len;
+}
+
 static char *
 w3m_dir(const char *name, char *dft)
 {