Delegate copy command to cmake binary.

The CMakeLists.txt was performing a `cp` command
directly, which while it was not an issue on linux,
if you build on Windows with cmake, it fails the
build because the equivalent command is `copy`.

I made it so we use the portable interface of
the CMake binary to perform the copy across all
targets, so it's portable.

Author: NlightNFotis

jbmc/CMakeLists.txt

@@ -4,7 +4,7 @@ add_subdirectory(unit)
 
 add_custom_target(java-models-library ALL
     COMMAND mvn --quiet -Dmaven.test.skip=true package
-    COMMAND cp target/core-models.jar ${CMAKE_CURRENT_SOURCE_DIR}/src/java_bytecode/library/
+    COMMAND ${CMAKE_COMMAND} -E copy target/core-models.jar ${CMAKE_CURRENT_SOURCE_DIR}/src/java_bytecode/library/
     WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/lib/java-models-library
 )