cmake: Use set_property( SOURCE ... COMPILE_DEFINITIONS )

instead of set_source_files_properties( ... COMPILE_FLAGS )
to avoid the problem of double escaping quotation marks.

Signed-off-by: Michele Calgaro <michele.calgaro@yahoo.it>

quanta/src/CMakeLists.txt

@@ -54,7 +54,7 @@ install( FILES x-webprj.desktop DESTINATION ${MIME_INSTALL_DIR}/application )
 
 ##### quanta (executable) #######################
 
-set_source_files_properties( kqapp.cpp PROPERTIES COMPILE_FLAGS -DPREFIX=\\"${CMAKE_INSTALL_PREFIX}\\" )
+set_property( SOURCE kqapp.cpp APPEND PROPERTY COMPILE_DEFINITIONS PREFIX="${CMAKE_INSTALL_PREFIX}" )
 
 tde_add_executable( quanta AUTOMOC
   SOURCES