[build] Update Slang dependency properties before installing (#9017)

The properties of Slang dependencies are updated to avoid installing their headers alongside our headers. However, the new properties are not correctly taken into account if we issue an install command before the update.

This commit fixes the update order in the main CMakeLists.txt file.

Author: jmgorius

CMakeLists.txt

@@ -604,12 +604,13 @@ if(CIRCT_SLANG_FRONTEND_ENABLED)
         get_target_property(dep_target ${dep_alias} ALIASED_TARGET)
         message(STATUS "Installing slang dependency ${dep_target}")
         set_property(GLOBAL APPEND PROPERTY CIRCT_EXPORTS ${dep_target})
-        install(TARGETS ${dep_target} EXPORT CIRCTTargets)
 
         # Disable the installation of headers coming from third-party libraries.
         # We won't use those APIs directly. Just make them static libraries for
         # the sake of running slang normally.
         set_target_properties(${dep_target} PROPERTIES PUBLIC_HEADER "")
+
+        install(TARGETS ${dep_target} EXPORT CIRCTTargets)
       endif()
     endforeach()
     set_property(GLOBAL APPEND PROPERTY CIRCT_EXPORTS slang_slang)