CMake: add target_link_libraries internally

Makes it easier to include glslang in a larger CMake project---instead
of having to call `target_link_libraries(glslang OSDependent OGLCompiler
HLSL)`, for example, you only need to call
`target_link_libraries(glslang)` and it will pull in the helpers it
needs.

This is also better in terms of cleaning up the "public interface",
of sorts, for building glslang: end-users probably shouldn't need to
know or be explicitly dependent on internal targets.

SPIRV/CMakeLists.txt

@@ -40,6 +40,7 @@ endif(ENABLE_NV_EXTENSIONS)
 
 add_library(SPIRV STATIC ${SOURCES} ${HEADERS})
 set_property(TARGET SPIRV PROPERTY FOLDER glslang)
+target_link_libraries(SPIRV glslang)
 
 add_library(SPVRemapper STATIC ${SPVREMAP_SOURCES} ${SPVREMAP_HEADERS})
 set_property(TARGET SPVRemapper PROPERTY FOLDER glslang)