message: Copies the source files for the header-only fmt library to the build directory.
diff: # Register the fmt header-only library for string formatting
  ############################################################
  -# Do not include these in the headers list even though they
  -# are included in the headers, it will cause CMake to try to
  -# compile them in anything that depends on fmt outside of this
  -# directory due to CMake's file property scope (directory based)
  -#set(fmt_sources
  -# fmt/format.cc
  -# fmt/ostream.cc
  -# )
  -
  set(fmt_headers
  fmt/format.h
  fmt/ostream.h
  fmt/printf.h
  )
  +# Do not include the following source files in the headers list even
  +# though they are explicitly included by the headers. It will cause CMake
  +# to try to compile them in anything that depends on fmt outside
  +# of this directory due to CMake's file property scope (directory based)
  +
  +set(fmt_headers_sources
  + fmt/format.cc
  + fmt/ostream.cc
  + )
  +
  blt_add_library(NAME fmt
  HEADERS ${fmt_headers}
  HEADERS_OUTPUT_SUBDIR fmt)
  @@ -45,6 +46,14 @@ install(DIRECTORY ${PROJECT_SOURCE_DIR}/thirdparty/fmt
  )
  install(EXPORT fmt-targets DESTINATION lib/cmake)
  +# Manually copy the souce files for the headers to the build directory
  +blt_copy_headers_target(
  + NAME fmt-headers-sources
  + HEADERS ${fmt_headers_sources}
  + DESTINATION $<BUILD_INTERFACE:${HEADER_INCLUDES_DIRECTORY}>/fmt)
  +add_dependencies(blt_copy_headers_fmt blt_copy_headers_fmt-headers-sources)
  +
  +
  set(FMT_FOUND TRUE CACHE INTERNAL "")
  mark_as_advanced(FMT_FOUND)
  