fix building of remaining binaries

the previous patch has removed the -DENABLE_EXPERIMENTAL flag, assuming
that it is not required any more without openscad_nogui being built.
while that is sufficient for the test suite, other binaries built in the
tests/ directory would still use those flags.

in order to make them buildable again, the -DOPENSCAD_NOGUI compile time
option is added (as the resulting binaries are command-line-only tools,
which was previously implicit by setting -DOPENSCAD_TESTING), and
-DENABLE_EXPERIMENTAL is restored.

tests/CMakeLists.txt

@@ -600,6 +600,8 @@ if (DEFINED OPENSCAD_DAY)
   add_definitions(-DOPENSCAD_DAY=${OPENSCAD_DAY})
 endif()
 
+add_definitions(-DENABLE_EXPERIMENTAL -DOPENSCAD_NOGUI)
+
 # Search for MCAD in correct place
 set(CTEST_ENVIRONMENT "${CTEST_ENVIRONMENT};OPENSCADPATH=${CMAKE_CURRENT_SOURCE_DIR}/../libraries")