Docs: add a 'pdf' cmake target.

We still don't build or ship a PDF PuTTY manual by default, but we may
as well conveniently expose Halibut's ability to do so.

(I don't guarantee the resulting PDF is particularly pretty -- some of
our overlong code lines do go off the right margin currently.)

(cherry picked from commit f9a8213d95)

doc/CMakeLists.txt

@@ -109,6 +109,13 @@ if(HALIBUT AND PERL_EXECUTABLE)
     WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
     DEPENDS ${manual_sources} ${manual_dependencies})
   list(APPEND doc_outputs puttydoc.txt)
+
+  # PDF. (We don't ship this; so it's only built on explicit request.)
+  add_custom_command(OUTPUT putty.pdf
+    COMMAND ${HALIBUT} --pdf ${manual_sources}
+    WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+    DEPENDS ${manual_sources} ${manual_dependencies})
+  add_custom_target(pdf DEPENDS putty.pdf)
 endif()
 
 macro(register_manpage title section)

doc/blurb.but

@@ -23,6 +23,7 @@ page</a>.</p>}
 \cfg{winhelp-filename}{putty.hlp}
 \cfg{info-filename}{putty.info}
 \cfg{chm-filename}{putty.chm}
+\cfg{pdf-filename}{putty.pdf}
 
 PuTTY is a free (MIT-licensed) Windows Telnet and SSH client. This
 manual documents PuTTY, and its companion utilities PSCP, PSFTP,