我有一个旧版本的 boost 1.33.1。我想使用自定义 gcc 二进制文件构建它，该二进制文件位于默认路径以外的路径中。我在网上找不到该页面，所以我粘贴了gcc-tools.jam表单的第一部分tools/build/v1/gcc-tools.jam。
版权所有 (c) 2001 大卫亚伯拉罕斯。
# Copyright (c) 2002-2005 Rene Rivera.
# Distributed under the Boost Software License, Version 1.0.
# (See accompanying file LICENSE_1_0.txt or http://www.boost.org/LICENSE_1_0.txt)
# The following #// line will be used by the regression test table generation
# program as the column heading for HTML tables. Must not include version number.
#//<a href="http://gcc.gnu.org/">GNU<br>GCC</a>
# compute directories for invoking GCC
#
# The gcc toolset can be user-configured using the following
# variables:
#
# GCC_ROOT_DIRECTORY
# The directory in which GCC was installed. Defaults to
# unset. Usually, there is no need to set this variable at
# all. However, if G++ is not in the path it is usually
# sufficient to configure this one variable. More fine-grained
# configuration is available by setting the following:
#
# GCC_BIN_DIRECTORY
# the directory prefix used to find the gcc executables. Defaults to
# $(GCC_ROOT_DIRECTORY)/bin/, or "" if GCC_ROOT_DIRECTORY is
# not set.
#
# GCC_INCLUDE_DIRECTORY
# the directory in which to find system includes. Defaults to
# empty.
#
# GCC_STDLIB_DIRECTORY
# the directory in which to find the standard library
# objects associated with this build of gcc. Defaults to
# $(GCC_ROOT_DIRECTORY)/lib.
#
# GXX
# The name by which g++ is invoked. You can also use this in
# lieu of setting the <cxxflags> property to force options such
# as "-V3.0.4" into the g++ command line: "-sGXX=g++ -V3.0.4".
#
# GCC
# Similar to GXX, the name by which gcc is invoked for "C"
# language targets.
# singleton variables...
set-as-singleton GCC_ROOT_DIRECTORY GCC_BIN_DIRECTORY GCC_INCLUDE_DIRECTORY GCC_STDLIB_DIRECTORY ;
flags gcc GCC_BIN_DIRECTORY : $(GCC_BIN_DIRECTORY) ;
flags gcc GCC_INCLUDE_DIRECTORY : $(GCC_INCLUDE_DIRECTORY) ;
flags gcc GCC_STDLIB_DIRECTORY : $(GCC_STDLIB_DIRECTORY) ;
GCC_BIN_DIRECTORY ?= $(GCC_ROOT_DIRECTORY)$(SLASH)bin ;
GCC_BIN_DIRECTORY ?= "" ; # Don't clobber tool names if GCC_ROOT_DIRECTORY not set
GCC_STDLIB_DIRECTORY ?= $(GCC_ROOT_DIRECTORY)$(SLASH)lib ;
# Make sure this gets set "on" the target
flags gcc GCC_BIN_DIR : $(GCC_BIN_DIRECTORY) ;
flags gcc LINKFLAGS <runtime-link>static : -static ;
flags gcc CFLAGS <debug-symbols>on : -g ;
flags gcc LINKFLAGS <debug-symbols>on : -g ;
flags gcc CFLAGS <optimization>off : -O0 ;
flags gcc CFLAGS <optimization>speed : -O3 ;
在这一部分中，我可以使用注释部分中定义的变量将默认的 gcc/g++ 修改为我自己的。但是我不知道该怎么做。例如，我写
GCC_BIN_DIRECTORY=/opt/gcc-4.1.2/installed
但这给了我这个错误：
rule GCC_ROOT_DIRECTORY=/opt/gcc-4.1.2/installed unknown in module
那么我该怎么做呢？