message: Remove BYPRODUCTS from cmake custom commands
  fixes ninja build error
  ninja: error: build.ninja:5574: multiple rules generate shader/sprv/shader.h [-w dupbuild=err]
  cmake documentation sounds like BYPRODUCTS is supposed to be used for intermediate files,
  not final outputs. It expliclity says "Byproducts may not be listed as outputs"
diff: @@ -25,7 +25,6 @@ function(add_shader OUTPUT SOURCE)
  list(SUBLIST ARGV 2 -1 VARS)
  add_custom_command(
  OUTPUT ${OUTPUT_FILE}
  - BYPRODUCTS ${OUTPUT_FILE}
  DEPENDS ${SOURCE_FILE}
  COMMAND ${CMAKE_COMMAND} -E make_directory "${PROJECT_BINARY_DIR}/sprv/"
  COMMAND ${GLSLANGVALIDATOR} -V ${VARS} "${SOURCE_FILE}" -o ${OUTPUT_FILE}
  @@ -97,7 +96,6 @@ add_shader(copy.frag copy.frag "")
  add_custom_command(
  OUTPUT ${HEADER} ${CPP}
  - BYPRODUCTS ${HEADER} ${CPP}
  DEPENDS ${OPENGOTHIC_SHADERS_SPRV}
  COMMAND ${CMAKE_COMMAND} -E make_directory "${PROJECT_BINARY_DIR}/sprv/"
  COMMAND ${CMAKE_COMMAND} -P "${CMAKE_SOURCE_DIR}/shader/link_shaders.cmake"
  