Only set include property on ll::bugpsplat target when on Windows.

The include was preveiously declared for all platforms, but the Mac
package does not even ship this include directory. With the new way
cmake works this will lead to an error (which is good, so we don't
end with bogus include dirs).

indra/cmake/bugsplat.cmake

@@ -19,6 +19,7 @@ if (USE_BUGSPLAT)
         target_link_libraries( ll::bugsplat INTERFACE
                 ${ARCH_PREBUILT_DIRS_RELEASE}/bugsplat.lib
                 )
+        target_include_directories( ll::bugsplat SYSTEM INTERFACE ${LIBS_PREBUILT_DIR}/include/bugsplat)
     elseif (DARWIN)
         find_library(BUGSPLAT_LIBRARIES BugsplatMac REQUIRED
                 NO_DEFAULT_PATH PATHS "${ARCH_PREBUILT_DIRS_RELEASE}")
@@ -33,7 +34,6 @@ if (USE_BUGSPLAT)
         message( FATAL_ERROR "You need to set BUGSPLAT_DB when setting USE_BUGSPLAT" )
     endif()
 
-    target_include_directories( ll::bugsplat SYSTEM INTERFACE ${LIBS_PREBUILT_DIR}/include/bugsplat)
     set_property( TARGET ll::bugsplat APPEND PROPERTY INTERFACE_COMPILE_DEFINITIONS LL_BUGSPLAT)
 else()
     set(BUGSPLAT_DB "" CACHE STRING "BugSplat crash database name")