Workaround for install step on Windows where symlinks might be not supported.
This leads to the following error:
CMake error : failed to create symbolic link ... : operation not permitted
--- a/c++/src/capnp/CMakeLists.txt
+++ b/c++/src/capnp/CMakeLists.txt
@@ -188,8 +188,12 @@ if(NOT CAPNP_LITE)
 
   install(TARGETS capnp_tool capnpc_cpp capnpc_capnp ${INSTALL_TARGETS_DEFAULT_ARGS})
 
-  # Symlink capnpc -> capnp
-  install(CODE "execute_process(COMMAND \"${CMAKE_COMMAND}\" -E create_symlink capnp${CMAKE_EXECUTABLE_SUFFIX} \"\$ENV{DESTDIR}${CMAKE_INSTALL_FULL_BINDIR}/capnpc${CMAKE_EXECUTABLE_SUFFIX}\")")
+  if(WIN32)
+    install(CODE "execute_process(COMMAND \"${CMAKE_COMMAND}\" -E copy \"\$ENV{DESTDIR}${CMAKE_INSTALL_FULL_BINDIR}/capnp${CMAKE_EXECUTABLE_SUFFIX}\" \"\$ENV{DESTDIR}${CMAKE_INSTALL_FULL_BINDIR}/capnpc${CMAKE_EXECUTABLE_SUFFIX}\")")
+  else()
+    # Symlink capnpc -> capnp
+    install(CODE "execute_process(COMMAND \"${CMAKE_COMMAND}\" -E create_symlink capnp${CMAKE_EXECUTABLE_SUFFIX} \"\$ENV{DESTDIR}${CMAKE_INSTALL_FULL_BINDIR}/capnpc${CMAKE_EXECUTABLE_SUFFIX}\")")
+  endif()
 endif()  # NOT CAPNP_LITE
 
 # Tests ========================================================================