add make target of 'dev_docs' which uses Doxygen to build html pages

This is not done by default, you need to manually type "make dev_docs"
in the configured build directory, as it takes ~6-8 min to build
everything.

Signed-off-by: Robin Getz <robin.getz@analog.com>

cmake/Modules/CheckCaseSensitiveFileSystem.cmake

@@ -0,0 +1,38 @@
+#
+# Check if the file system is case sensitive or not
+# Inspired by Andreas Lauser's cmake at:
+# https://github.com/OPM/opm-parser/blob/master/cmake/Modules/CheckCaseSensitiveFileSystem.cmake
+# Included in sdrangle (LGPL3) - with permission.
+#
+# Sets the following variable:
+# HAVE_CASE_SENSITIVE_FILESYSTEM   True if the file system honors the case of files
+#
+# I dislike that we have to emit a file from CMake, but I can't think of a better way.
+
+message(STATUS "Check for case-sensitive file systems")
+string(RANDOM LENGTH 6 ALPHABET abcdefghijklmnopqrstuvwxyz TMP_FILE_L)
+set(TMP_FILE_L "${TMP_FILE_L}.tmp")
+string(TOUPPER ${TMP_FILE_L} TMP_FILE_U)
+string(TIMESTAMP TMP_TIME)
+set(TMP_FILE_CONTENTS "${TMP_FILE_L} ${TMP_TIME}")
+# create a uppercase file
+file(WRITE "${CMAKE_BINARY_DIR}/${TMP_FILE_U}" "${TMP_FILE_CONTENTS}")
+
+# test if lowercase file can be opened
+set(FileContents "")
+if (EXISTS "${CMAKE_BINARY_DIR}/${TMP_FILE_L}")
+	file(READ "${CMAKE_BINARY_DIR}/${TMP_FILE_L}" FileContents)
+endif()
+
+# remove the file
+file(REMOVE "${CMAKE_BINARY_DIR}/${TMP_FILE_U}")
+
+# check the contents
+# If it is empty, the file system is case sensitive.
+if ("${FileContents}" STREQUAL "${TMP_FILE_CONTENTS}")
+	message(STATUS "File system is not case-sensitive")
+	set(HAVE_CASE_SENSITIVE_FILESYSTEM 0)
+else()
+	message(STATUS "File system is case-sensitive")
+	set(HAVE_CASE_SENSITIVE_FILESYSTEM 1)
+endif()