CMake Stop forcing OMR_SEPARATE_DEBUG_INFO

Setting a cache variable as internal force-overwrites its previous value.
Leaving as a normal set() means that the user is able to override it on
the command line. This is useful when making a local debug build, as
debuggers don't always play nice with the split debug info.

Signed-off-by: Devin Nakamura <devinn@ca.ibm.com>

runtime/cmake/omr_config.cmake

@@ -28,5 +28,5 @@ set(OMR_DDR OFF CACHE BOOL "")
 set(OMR_EXAMPLE OFF CACHE INTERNAL "")
 set(OMR_FVTEST OFF CACHE INTERNAL "")
 set(OMR_GC ON CACHE INTERNAL "")
-set(OMR_SEPARATE_DEBUG_INFO ON CACHE INTERNAL "")
+set(OMR_SEPARATE_DEBUG_INFO ON CACHE BOOL "")
 set(OMRPORT_OMRSIG_SUPPORT ON CACHE INTERNAL "")