While compiling libtorrent-0.12.2 and rtorrent-0.8.2 on CentOS 5 32 i386 the following error was obtained while compiling rtorrent.

checking for STUFF... configure: error: Package requirements (sigc++-2.0 libcurl >= 7.12.0 libtorrent >= 0.12.2) were not met:

No package 'libtorrent' found

Consider adjusting the PKG_CONFIG_PATH environment variable if you
installed software in a non-standard prefix.

Alternatively, you may set the environment variables STUFF_CFLAGS
and STUFF_LIBS to avoid the need to call pkg-config.
See the pkg-config man page for more details.

The fix was just sym-linking the libtorrent.pc file into the correct pkgconfig directory. Afterwards it compiled fine.

ln -s /usr/local/lib/pkgconfig/libtorrent.pc /usr/lib/pkgconfig/