Squashed 'external/fmt/' content from commit e1832bcf

git-subtree-dir: external/fmt
git-subtree-split: e1832bcf00ed53048aea1e4d2408a68301dcd50c

doc/CMakeLists.txt

@@ -0,0 +1,26 @@
+find_program(DOXYGEN doxygen
+  PATHS "$ENV{ProgramFiles}/doxygen/bin"
+        "$ENV{ProgramFiles\(x86\)}/doxygen/bin")
+if (NOT DOXYGEN)
+  message(STATUS "Target 'doc' disabled (requires doxygen)")
+  return ()
+endif ()
+
+# Find the Python interpreter and set the PYTHON_EXECUTABLE variable.
+if (CMAKE_VERSION VERSION_LESS 3.12)
+  # This logic is deprecated in CMake after 3.12.
+  find_package(PythonInterp QUIET REQUIRED)
+else ()
+  find_package(Python QUIET REQUIRED)
+  set(PYTHON_EXECUTABLE ${Python_EXECUTABLE})
+endif ()
+
+add_custom_target(doc
+  COMMAND ${PYTHON_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/build.py
+                               ${FMT_VERSION}
+  SOURCES api.rst syntax.rst usage.rst build.py conf.py _templates/layout.html)
+
+include(GNUInstallDirs)
+install(DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/html/
+        DESTINATION ${CMAKE_INSTALL_DATAROOTDIR}/doc/fmt OPTIONAL
+        PATTERN ".doctrees" EXCLUDE)