build: more fine-grained dependencies for documentation build tools

Perl is needed to build the manual pages, texi2html for the HTML pages.

configure

@@ -1107,7 +1107,6 @@ CONFIG_LIST="
     $LIBRARY_LIST
     $PROGRAM_LIST
     dct
-    doc
     error_resilience
     fft
     gpl
@@ -1119,6 +1118,7 @@ CONFIG_LIST="
     memalign_hack
     network
     nonfree
+    perl
     pic
     rdft
     runtime_cpudetect
@@ -1128,6 +1128,7 @@ CONFIG_LIST="
     sram
     static
     swscale_alpha
+    texi2html
     thumb
     version3
     xmm_clobber_test
@@ -1963,8 +1964,6 @@ avserver_deps="avformat fork !shared"
 avserver_select="ffm_muxer rtp_protocol rtsp_demuxer"
 avserver_extralibs='$ldl'
 
-doc_deps="texi2html"
-
 # default parameters
 
 logfile="config.log"
@@ -3869,6 +3868,7 @@ if check_pkg_config sdl SDL_events.h SDL_PollEvent; then
     enable sdl
 fi
 
+perl -v            > /dev/null 2>&1 && enable perl      || disable perl
 texi2html -version > /dev/null 2>&1 && enable texi2html || disable texi2html
 
 check_header linux/fb.h

doc/Makefile

@@ -10,9 +10,11 @@ HTMLPAGES   = $(PROGS-yes:%=doc/%.html)                                 \
               doc/nut.html                                              \
               doc/platform.html                                         \
 
-DOCS = $(HTMLPAGES) $(MANPAGES) $(PODPAGES)
+DOCS-$(CONFIG_PERL)                             += $(MANPAGES) $(PODPAGES)
+DOCS-$(CONFIG_TEXI2HTML)                        += $(HTMLPAGES)
+DOCS = $(DOCS-yes)
 
-all-$(CONFIG_DOC): documentation
+all: $(DOCS)
 
 apidoc: doc/doxy/html
 documentation: $(DOCS)
@@ -45,7 +47,8 @@ $(DOCS) doc/doxy/html: | doc/
 doc/doxy/html: $(SRC_PATH)/doc/Doxyfile $(INSTHEADERS)
 	$(M)$(SRC_PATH)/doc/doxy-wrapper.sh $(SRC_PATH) $^
 
-install-progs-$(CONFIG_DOC): install-doc install-man
+install-progs-$(CONFIG_PERL): install-man
+install-progs-$(CONFIG_TEXI2HTML): install-doc
 
 install-doc: $(HTMLPAGES)
 	$(Q)mkdir -p "$(DOCDIR)"