Ubuntuで試してみました。
きちんとlibexpat-devがインストールされていれば以下のようなファイルがあるはずです。
/usr/lib/x86_64-linux-gnu/libexpat.la
/usr/lib/x86_64-linux-gnu/libexpatw.so.1.5.2
/usr/lib/x86_64-linux-gnu/libexpatw.la
/usr/lib/x86_64-linux-gnu/libexpat.a
/usr/lib/x86_64-linux-gnu/libexpatw.a

/usr/include/expat_config.h
/usr/include/expat.h
/usr/include/expat_external.h

cmake も特にエラーなく終了します。

Ubuntu:~/Scalable/qualnet/7.2> cmake .
-- The C compiler identification is GNU
-- The CXX compiler identification is GNU
-- Check for working C compiler: /usr/bin/gcc
-- Check for working C compiler: /usr/bin/gcc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Found glibc version: 2.15
-- Found gcc version: 4.6
-- Found build platform: linux-x64-glibc-2.15-gcc-4.6
-- Could NOT find TIREM (missing: TIREM_INCLUDE_DIR TIREM_LIBRARY)
-- Could NOT find VRLINK (missing: VRLINK_INCLUDE_DIR VRLINK_VLUTIL_LIBRARY VRLINK_VL_LIBRARY VRLINK_MATRIX_LIBRARY VRLINK_MTL_LIBRARY VRLINK_VLDIS_LIBRARY VRLINK_VLHLA13_LIBRARY VRLINK_VLHLA1516_LIBRARY)
-- Could NOT find MAKRTI (missing: MAKRTI_INCLUDE_DIR MAKRTI_HLA13_INCLUDE_DIR MAKRTI_HLA1516_INCLUDE_DIR MAKRTI_RTI_NG_LIBRARY MAKRTI_FEDTIME_LIBRARY MAKRTI_RTI1516_LIBRARY MAKRTI_FEDTIME1516_LIBRARY)
-- Could NOT find Boost
-- Found EXPAT: /usr/lib/x86_64-linux-gnu/libexpat.so
-- Could NOT find MYSQL (missing: MYSQL_LIBRARY MYSQL_INCLUDE_DIR)
-- Found SQLite3: /usr/lib/x86_64-linux-gnu/libsqlite3.so (found version "3.7.9")
-- Found Perl: /usr/bin/perl
-- Could NOT find Doxygen (missing: DOXYGEN_EXECUTABLE)
--

-- The following features have been enabled:

* vrlink , Interface to federated simulation
* testsuite , Run the regression testsuite with "make test"

-- The following OPTIONAL packages have been found:

* EXPAT
* SQLite3
* Perl

-- The following features have been disabled:

* tirem , TIREM propagation model
* interfacetutorial , Interface tutorial
* ctdb , CTDB terrain model
* contrib_maodv , Contributed MAODV model
* apidocs , Build API documentation with "make apidocs"

-- The following OPTIONAL packages have not been found:

* TIREM
* VRLink
* MAKRTI
* Boost (required version >= 1.49)
* MYSQL
* Doxygen
-- Configuring done
-- Generating done
-- Build files have been written to: /home/hiro/Scalable/qualnet/7.2