Makefile.am: avoid parallelizing "doc" and "all-recursive" just in ca…

…se (only follow up by "make doc")

Maybe this is behind duplicate man page builds which
tend to step on each other's toes.

Signed-off-by: Jim Klimov <jimklimov+nut@gmail.com>

Makefile.am

@@ -15,7 +15,8 @@
 # missing e.g. PDF and HTML which then pop up in `make check` footprint,
 # or misses a .prep-src-docs stage needed to pattern-make man page files
 # with some "make" implementations...
-all all-am-local all-local: doc all-recursive
+all all-am-local all-local: all-recursive
+	+@$(MAKE) $(AM_MAKEFLAGS) doc
 	+@$(MAKE) $(AM_MAKEFLAGS) doc
 
 # include directory for aclocal