docs: Ignore Sphinx doctrees produced by manpage build

Test Plan: Validate

Reviewers: austin

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1491

.gitignore

@@ -98,8 +98,7 @@ _darcs/
 /docs/users_guide/users_guide.pdf
 /docs/users_guide/build-html
 /docs/users_guide/build-pdf
-/docs/users_guide/.doctrees-html
-/docs/users_guide/.doctrees-pdf
+/docs/users_guide/.doctrees-*
 /driver/ghci/ghc-pkg-inplace
 /driver/ghci/ghci-inplace
 /driver/ghci/ghci.res

docs/users_guide/ghc.mk

@@ -27,7 +27,7 @@ MAN_PAGES := docs/users_guide/ghc.1
 
 ifneq "$(BINDIST)" "YES"
 $(MAN_PAGES): $(docs/users_guide_MAN_RST_SOURCES) $(utils/mkUserGuidePart_GENERATED_RST_SOURCES)
-	$(SPHINXBUILD) -b man docs/users_guide docs/users_guide
+	$(SPHINXBUILD) -b man -d docs/users_guide/.doctrees-man docs/users_guide docs/users_guide
 endif
 
 man : $(MAN_PAGES)