configure: error: you must configure in a separate build directory

[root@localhost opt]# cd glibc-2.14
[root@localhost glibc-2.14]# ./configure
checking build system type... x86_64-unknown-linux-gnu
checking host system type... x86_64-unknown-linux-gnu
checking for gcc... gcc
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether gcc accepts -g... yes
checking for gcc option to accept ISO C89... none needed
checking how to run the C preprocessor... gcc -E
checking for g++... g++
checking whether we are using the GNU C++ compiler... yes
checking whether g++ accepts -g... yes
configure: error: you must configure in a separate build directory

[root@localhost glibc-2.14]# cd ../
[root@localhost opt]# ./glibc-2.14/configure