cmake: add support for building HTML and PDF docs

Note that for some reason there is this warning (that also exists with
autotools, added since curl-7_15_1-94-ga718cb05f):

    docs/libcurl/curl_multi_socket_all.3:1: can't open `man3/curl_multi_socket.3': No such file or directory

Additionally, adjust the roffit --mandir option to support creating
links when doing out-of-tree builds.

Ref: https://github.com/curl/curl/pull/1288

docs/CMakeLists.txt

@@ -1,3 +1,3 @@
 #add_subdirectory(examples)
-#add_subdirectory(libcurl)
+add_subdirectory(libcurl)
 add_subdirectory(cmdline-opts)

docs/libcurl/CMakeLists.txt

@@ -0,0 +1,55 @@
+# Load man_MANS from shared file
+transform_makefile_inc("Makefile.inc" "${CMAKE_CURRENT_BINARY_DIR}/Makefile.inc.cmake")
+include("${CMAKE_CURRENT_BINARY_DIR}/Makefile.inc.cmake")
+
+function(add_manual_pages _listname)
+  foreach(_file IN LISTS ${_listname})
+    if(_file STREQUAL "libcurl-symbols.3")
+      # Special case, an auto-generated file.
+      set(_srcfile "${CMAKE_CURRENT_BINARY_DIR}/${_file}")
+    else()
+      set(_srcfile "${CMAKE_CURRENT_SOURCE_DIR}/${_file}")
+    endif()
+
+    string(REPLACE ".3" ".html" _htmlfile "${CMAKE_CURRENT_BINARY_DIR}/${_file}")
+    add_custom_command(OUTPUT "${_htmlfile}"
+      COMMAND roffit "--mandir=${CMAKE_CURRENT_SOURCE_DIR}" "${_srcfile}" > "${_htmlfile}"
+      DEPENDS "${_srcfile}"
+      VERBATIM
+    )
+
+    string(REPLACE ".3" ".pdf" _pdffile "${CMAKE_CURRENT_BINARY_DIR}/${_file}")
+    string(REPLACE ".3" ".ps" _psfile "${CMAKE_CURRENT_BINARY_DIR}/${_file}")
+    # XXX any reason why groff -Tpdf (for gropdf) is not used?
+    add_custom_command(OUTPUT "${_pdffile}"
+      COMMAND groff -Tps -man "${_srcfile}" > "${_psfile}"
+      COMMAND ps2pdf "${_psfile}" "${_pdffile}"
+      COMMAND "${CMAKE_COMMAND}" -E remove "${_psfile}"
+      DEPENDS "${_srcfile}"
+      #BYPRODUCTS "${_psfile}"
+      VERBATIM
+    )
+    # "BYPRODUCTS" for add_custom_command requires CMake 3.2. For now hope that
+    # the temporary files are removed (i.e. the command is not interrupted).
+  endforeach()
+endfunction()
+
+add_custom_command(OUTPUT libcurl-symbols.3
+  COMMAND
+    "${PERL_EXECUTABLE}"
+    "${CMAKE_CURRENT_SOURCE_DIR}/mksymbolsmanpage.pl" <
+    "${CMAKE_CURRENT_SOURCE_DIR}/symbols-in-versions" > libcurl-symbols.3
+  DEPENDS
+    "${CMAKE_CURRENT_SOURCE_DIR}/symbols-in-versions"
+    "${CMAKE_CURRENT_SOURCE_DIR}/mksymbolsmanpage.pl"
+  VERBATIM
+)
+
+add_manual_pages(man_MANS)
+
+string(REPLACE ".3" ".html" HTMLPAGES "${man_MANS}")
+string(REPLACE ".3" ".pdf" PDFPAGES "${man_MANS}")
+add_custom_target(html DEPENDS "${HTMLPAGES}")
+add_custom_target(pdf DEPENDS "${PDFPAGES}")
+
+add_subdirectory(opts)

docs/libcurl/opts/CMakeLists.txt

@@ -0,0 +1,12 @@
+# Load man_MANS from shared file
+transform_makefile_inc("Makefile.inc" "${CMAKE_CURRENT_BINARY_DIR}/Makefile.inc.cmake")
+include("${CMAKE_CURRENT_BINARY_DIR}/Makefile.inc.cmake")
+
+add_manual_pages(man_MANS)
+
+string(REPLACE ".3" ".html" HTMLPAGES "${man_MANS}")
+string(REPLACE ".3" ".pdf" PDFPAGES "${man_MANS}")
+add_custom_target(opts-html DEPENDS "${HTMLPAGES}")
+add_custom_target(opts-pdf DEPENDS "${PDFPAGES}")
+add_dependencies(html opts-html)
+add_dependencies(pdf opts-pdf)