[PATCH] doc: Makefile: stop build notmuch-emacs.info when not have emacs

[Doan Tran Cong Danh]

Current behavior:
- When build on system without emacs:

./configure --without-emacs
make
make install

`make install` failed with:
> /usr/bin/install: cannot stat 'doc/_build/texinfo/notmuch-emacs.info': No such file or directory

Signed-off-by: Doan Tran Cong Danh <congdanhqx at gmail.com>
---
I don't know if this is a _good_ fix for this issue.
This is my quick-and-dirty patch to package notmuch for Void Linux.
 doc/Makefile.local | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/doc/Makefile.local b/doc/Makefile.local
index 719172fe..732d92f5 100644
--- a/doc/Makefile.local
+++ b/doc/Makefile.local
@@ -28,7 +28,10 @@ MAN_GZIP_FILES := $(addsuffix .gz,${MAN_ROFF_FILES})
 MAN1_TEXI := $(patsubst $(srcdir)/doc/man1/%.rst,$(DOCBUILDDIR)/texinfo/%.texi,$(MAN1_RST))
 MAN5_TEXI := $(patsubst $(srcdir)/doc/man5/%.rst,$(DOCBUILDDIR)/texinfo/%.texi,$(MAN5_RST))
 MAN7_TEXI := $(patsubst $(srcdir)/doc/man7/%.rst,$(DOCBUILDDIR)/texinfo/%.texi,$(MAN7_RST))
-INFO_TEXI_FILES := $(MAN1_TEXI) $(MAN5_TEXI) $(MAN7_TEXI) $(DOCBUILDDIR)/texinfo/notmuch-emacs.texi
+INFO_TEXI_FILES := $(MAN1_TEXI) $(MAN5_TEXI) $(MAN7_TEXI)
+ifeq ($(WITH_EMACS),1)
+INFO_TEXI_FILES := $(INFO_TEXI_FILES) $(DOCBUILDDIR)/texinfo/notmuch-emacs.texi
+endif
 INFO_INFO_FILES := $(INFO_TEXI_FILES:.texi=.info)
 
 .PHONY: sphinx-html sphinx-texinfo sphinx-info
-- 
2.22.0.rc1.479.gd8fdbe21b5