I know the reason of your error,
you should use:

cpack -D CPACK_SET_DESTDIR=ON -G RPM
or
SET(CPACK_SET_DESTDIR ON) in tsp/CMakeLists.txt

see
http://public.kitware.com/Bug/view.php?id=7000

sorry for the delay but I did not have this bug
because I use a patched CMake version...

With the current CVS version,
if you run

cmake -DCMAKE_INSTALL_PREFIX=/opt
then
make
cpack -G RPM
you should have a clean RPM content regarding tsp.pc
(cpack -G RPM needs CMake 2.6.x in order to be available)

Note that if you don't specify CMAKE_INSTALL_PREFIX
then the default value is /usr.

Now if you do use:
make tsp_rpm  (and not cpack -G RPM)
then I have an unidentified trouble...

I noticed the bug using the sources located at this URL :

http://download.savannah.gnu.org/releases/tsp/tsp-0.8.x/tsp-0.8.3/sources/tsp-0.8.3-Source.tar.gz

With theses sources, the tsp.pc file is generated using the macro CMAKE_INSTALL_PREFIX which gives the result that I reported opening the ticket. I think there is a gap between the CVS and the repo.

Considering your comment, I replaced the tsp.pc.in file by the one you told me.

With this version the tsp.pc is generated with an empty value for the prefix. Is there a specific parameter to use with cmake in order to intialize the macro ?

The prefix path contained in the generated tsp.pc file when the RPM for tsp built is incorrect.

It should be the target directory on the system where the RPM is installed in stead of being the RPM environment build directory.

tsp.pc snapshot generated with tsp_rpm target
----------------------------------------------

prefix=/home/olivier/tsp/tsp_build/RPM/tmp/opt/tsp-0.8.3
exec_prefix=/home/olivier/tsp/tsp_build/RPM/tmp/opt/tsp-0.8.3/bin
libdir=/home/olivier/tsp/tsp_build/RPM/tmp/opt/tsp-0.8.3/lib
includedir=/home/olivier/tsp/tsp_build/RPM/tmp/opt/tsp-0.8.3/incl

The prefix should be /opt/tsp-0.8.3 and not /home/olivier/tsp/tsp_build/RPM/tmp/opt/tsp-0.8.3.