[CMake] add_llvm_library: don't use .imp suffix for import libraries on Windows (PR22334)

[hans]

Summary

This was added in r188351 to fix a naming conflict between the profile_rt-static and profile_rt-shared who both ended up in lib/profile_rt.lib.

The change also affected other libraries (like libclang), and users are reporting that they find it surprising that there's no longer a libclang.lib. Since the profile_rt naming conflict doesn't seem to exist any more, I think we can remove this.

[rnk]

lgtm

My build of compiler-rt configures without warnings. :)

llvm/trunk/cmake/modules/AddLLVM.cmake

function(llvm_add_library name)
   endif()
 
   if(ARG_SHARED)
     if(WIN32)
       set_target_properties(${name} PROPERTIES
         PREFIX ""
         )
     endif()
-    if (MSVC)
-      set_target_properties(${name}
-        PROPERTIES
-        IMPORT_SUFFIX ".imp")
-    endif ()
   endif()
 
   if(ARG_MODULE OR ARG_SHARED)
     # Do not add -Dname_EXPORTS to the command-line when building files in this
     # target. Doing so is actively harmful for the modules build because it
     # creates extra module variants, and not useful because we don't use these
     # macros.
     set_target_properties( ${name} PROPERTIES DEFINE_SYMBOL "" )