DirectX Raytracing Binaries Release V1.5

Add 'export' keyword for lib_6_3 compatibility (#471)

In a previous commit, this branch was updated to target lib_6_3 from lib_6_1.
6_3 differs from 6_1 in that it doesn’t export all functions by default. You need to either use ‘export’ (the keyword) or use the -default-linkage option. This change adds the 'export' keyword where necessary.