[PATCH nft] build: fix tentative generation of nft.8 after disabled doc

[Laura Garcia Liebana <nevola@gmail.com>]

Despite doc generation is disabled, the makefile is trying to build it.

$ ./configure --disable-man-doc
$ make
Making all in doc
make[2]: Entering directory '/workdir/build-pkg/workdir/doc'
make[2]: *** No rule to make target 'nft.8', needed by 'all-am'.  Stop.
make[2]: Leaving directory '/workdir/build-pkg/workdir/doc'
make[1]: *** [Makefile:479: all-recursive] Error 1
make[1]: Leaving directory '/workdir/build-pkg/workdir'
make: *** [Makefile:388: all] Error 2

Fixes: 4f2813a313ae0 ("build: Include generated man pages in dist tarball")

Reported-by: Adan Marin Jacquot <adan.marin@zevenet.com>
Signed-off-by: Laura Garcia Liebana <nevola@gmail.com>
---
 doc/Makefile.am | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/Makefile.am b/doc/Makefile.am
index 6bd90aa6..21482320 100644
--- a/doc/Makefile.am
+++ b/doc/Makefile.am
@@ -1,3 +1,4 @@
+if BUILD_MAN
 man_MANS = nft.8 libnftables-json.5 libnftables.3
 
 A2X_OPTS_MANPAGE = -L --doctype manpage --format manpage -D ${builddir}
@@ -16,7 +17,6 @@ EXTRA_DIST = ${ASCIIDOCS} ${man_MANS} libnftables-json.adoc libnftables.adoc
 CLEANFILES = \
 	*~
 
-if BUILD_MAN
 nft.8: ${ASCIIDOCS}
 	${AM_V_GEN}${A2X} ${A2X_OPTS_MANPAGE} $<
 
-- 
2.20.1