[lld-macho] Fix BUILD_SHARED_LIBS build

ca6751043d added a dependency on XAR (at
least for the shared libs build), so without this change we get the
following linker error:

Undefined symbols for architecture x86_64:
  "_xar_close", referenced from:
      lld::macho::BitcodeBundleSection::finalize() in SyntheticSections.cpp.o

Reviewed By: #lld-macho, int3, thakis

Differential Revision: https://reviews.llvm.org/D100999

lld/MachO/CMakeLists.txt

@@ -55,3 +55,7 @@ add_lld_library(lldMachO2
   MachOOptionsTableGen
   ${tablegen_deps}
   )
+
+if(LLVM_HAVE_LIBXAR)
+  target_link_libraries(lldMachO2 PRIVATE ${XAR_LIB})
+endif()

lld/tools/lld/CMakeLists.txt

@@ -20,10 +20,6 @@ target_link_libraries(lld
   lldWasm
   )
 
-if(LLVM_HAVE_LIBXAR)
-  target_link_libraries(lld PRIVATE ${XAR_LIB})
-endif()
-
 install(TARGETS lld
   RUNTIME DESTINATION bin)