Update RPM spec for building on CentOS6.

scripts/rpm-data/klayout.spec

@@ -40,7 +40,10 @@ Requires: qt-x11 >= 4.8.5
 
 %if "%{target_system}" == "centos6"
 # CentOS6 requirements
-# ...
+Requires: libcurl >= 7.19.7
+Requires: ruby >= 1.8.7
+Requires: python >= 2.6.6
+BUILDOPT="-libcurl"
 %endif
 
 %if "%{target_system}" == "opensuse42_2"
@@ -86,6 +89,7 @@ cd %{_sourcedir}
 ./build.sh -rpath %{_libdir}/klayout \
            -bin %{_builddir}/bin.$TARGET \
            -build %{_builddir}/build.$TARGET \
+           $BUILDOPT \
            -j2 
 
 cp -p LICENSE Changelog CONTRIB %{_builddir}