为了支持交叉编译，可能需要修改的内容项目
一.需要修改的变量：
CC C compiler command
CFLAGS C compiler flags
LDFLAGS linker flags, e.g. -L<lib dir> if you have libraries in a
nonstandard directory <lib dir>
LIBS libraries to pass to the linker, e.g. -l<library>
CPPFLAGS C/C++/Objective C preprocessor flags, e.g. -I<include dir> if
you have headers in a nonstandard directory <include dir>
Use these variables to override the choices made by `configure’ or to help
it to find libraries and programs with nonstandard names/locations.
二.需要修改的软件包
有些工具可能需要修改，比如生成二进制文件的工具，需要特殊的面向目标平台的链接程序等、
configure文件内容：
# 相关变量
# Initializations.
#
#安装目录选项，即将来的文件在make install exec_prefix=/foo会安装这个
#设置进行安装，为了达到这个效果，需要设置的变量
# Installation directory options.
#交叉编译涉及的变量
build=$build_alias
host=$host_alias
target=$target_alias
处理命令行configure参数的一堆：
‘–host=HOST’
指定软件运行的系统平台.如果没有指定,将会运行`config.guess’来检测.
‘–target=GARGET’
指定软件面向(target to)的系统平台.这主要在程序语言工具如编译器和汇编器上下文中起作用.如果没有指定,默认将使用’–host’选项的值.
#查找源文件
# Find the source files, if location was not specified.
#显示help信息的部分，包括help信息内容
# Report the –help message.
Some influential environment variables:
CC C compiler command
CFLAGS C compiler flags
LDFLAGS linker flags, e.g. -L<lib dir> if you have libraries in a
nonstandard directory <lib dir>
LIBS libraries to pass to the linker, e.g. -l<library>
CPPFLAGS C/C++/Objective C preprocessor flags, e.g. -I<include dir> if
you have headers in a nonstandard directory <include dir>
Use these variables to override the choices made by `configure’ or to help
it to find libraries and programs with nonstandard names/locations.