sci-misc/stable-diffusion-cpp: media-libs/shaderc is only needed for ggml-vulkan

Signed-off-by: Gilles Dartiguelongue <gilles.dartiguelongue@esiee.org>

sci-misc/stable-diffusion-cpp/stable-diffusion-cpp-9999.ebuild

@@ -85,7 +85,7 @@ RDEPEND="${COMMON_DEPEND}
 	opencl? ( dev-libs/opencl-icd-loader )
 	vulkan? ( media-libs/vulkan-loader )
 "
-BDEPEND="media-libs/shaderc"
+BDEPEND="vulkan? ( media-libs/shaderc )"
 
 pkg_pretend() {
 	[[ ${MERGE_TYPE} != binary ]] && use openmp && tc-check-openmp