configure: Modify ERROR to WARN for sphinx's python check

If sphinx's python version check failed, many people prefer to build
without documents instead of stopping on the error.

So this commit fixes the following:

* Modify AC_MSG_ERROR to AC_MSG_WARN
* Add clearing of SPHINXBUILD variable when check fails

See also !2016.
23 jobs for master in 591 minutes and 25 seconds (queued for 43 seconds)
Status Name Job ID Coverage
  Lint
passed lint-linters #194679
lint

00:00:16

passed lint-submods-branch #194682
lint

00:00:21

passed lint-testsuite #194680
lint

00:00:20

passed typecheck-testsuite #194681
lint

00:00:20

 
  Quick Build
passed hadrian-ghc-in-ghci #194683
x86_64-linux

00:14:53

 
  Build
passed release-x86_64-linux-deb9-dwarf #194686
x86_64-linux

02:06:38

passed validate-x86_64-linux-deb9-debug #194685
x86_64-linux

02:46:14

passed validate-x86_64-linux-deb9-hadrian #195050
x86_64-linux

02:24:24

failed validate-x86_64-linux-deb9-hadrian #194684
x86_64-linux

00:40:52

 
  Full Build
failed validate-aarch64-linux-deb9 #194689
aarch64-linux allowed to fail

03:46:02

failed validate-armv7-linux-deb9 #194690
armv7-linux allowed to fail

03:30:24

passed validate-i386-linux-deb9 #194691
x86_64-linux

01:31:14

passed validate-x86_64-darwin #194688
x86_64-darwin

00:48:48

passed validate-x86_64-linux-deb9-integer-simple #194692
x86_64-linux

01:06:31

passed validate-x86_64-linux-deb9-unreg-hadrian #194687
x86_64-linux

02:28:00

passed validate-x86_64-linux-fedora27 #194693
x86_64-linux

01:56:47

failed validate-x86_64-windows #194695
x86_64-windows allowed to fail

00:09:37

failed validate-x86_64-windows-hadrian #194694
x86_64-windows allowed to fail

00:29:45

 
  Cleanup
passed cleanup-darwin #194696
x86_64-darwin

00:00:05

 
  Packaging
failed doc-tarball #194697
x86_64-linux allowed to fail

00:01:22

 
  Testing
manual hackage #194698
x86_64-linux allowed to fail manual
passed perf-nofib #194699
x86_64-linux

00:35:36

 
  Deploy
failed pages #194700
x86_64-linux allowed to fail

00:01:42

 
Name Stage Failure
failed
validate-aarch64-linux-deb9 Full Build
Uploading artifacts...
ghc-aarch64-linux-deb9.tar.xz: found 1 matching files
junit.xml: found 1 matching files

performance-metrics.tsv: found 1 matching files

Uploading artifacts to coordinator... ok
id=194689 responseStatus=201 Created token=9VzMkwc9
Uploading artifacts...
junit.xml: found 1 matching files

Uploading artifacts to coordinator... ok
id=194689 responseStatus=201 Created token=9VzMkwc9
ERROR: Job failed: exit code 1
failed
validate-armv7-linux-deb9 Full Build
Uploading artifacts...
ghc-armv7-linux-deb9.tar.xz: found 1 matching files
junit.xml: found 1 matching files

performance-metrics.tsv: found 1 matching files

Uploading artifacts to coordinator... ok
id=194690 responseStatus=201 Created token=N-5KoSBm
Uploading artifacts...
junit.xml: found 1 matching files

Uploading artifacts to coordinator... ok
id=194690 responseStatus=201 Created token=N-5KoSBm
ERROR: Job failed: exit code 1
failed
validate-x86_64-windows-hadrian Full Build
Runtime platform                                    arch=amd64 os=windows pid=3140 revision=1f513601 version=11.10.1
WARNING: ghc.tar.xz: no matching files
WARNING: junit.xml: no matching files
ERROR: No files to upload
Uploading artifacts...
Runtime platform
arch=amd64 os=windows pid=6960 revision=1f513601 version=11.10.1
WARNING: junit.xml: no matching files
ERROR: No files to upload
ERROR: Job failed: exit status 1
failed
validate-x86_64-windows Full Build
Runtime platform                                    arch=amd64 os=windows pid=5772 revision=1f513601 version=11.10.1
WARNING: $BIN_DIST_PREP_TAR_COMP: no matching files
WARNING: junit.xml: no matching files
ERROR: No files to upload
Uploading artifacts...
Runtime platform
arch=amd64 os=windows pid=2816 revision=1f513601 version=11.10.1
WARNING: junit.xml: no matching files
ERROR: No files to upload
ERROR: Job failed: exit status 2
failed
doc-tarball Packaging
Submodule path 'utils/hsc2hs': checked out '4c65964de3ca1a002901cae95217ad10b95edeeb'
$ git checkout .gitmodules
$ git fetch https://gitlab.haskell.org/ghc/ghc-performance-notes.git refs/notes/perf:refs/notes/perf || true
warning: no common commits
From https://gitlab.haskell.org/ghc/ghc-performance-notes
* [new ref] refs/notes/perf -> refs/notes/perf
$ if [ ! -f "$LINUX_BINDIST" ]; then # collapsed multi-line command
Error: ghc-x86_64-mingw32.tar.xz does not exist. Did the 64-bit Windows job fail?
ERROR: Job failed: exit code 1
failed
pages Deploy
$ git checkout .gitmodules
$ git fetch https://gitlab.haskell.org/ghc/ghc-performance-notes.git refs/notes/perf:refs/notes/perf || true
From https://gitlab.haskell.org/ghc/ghc-performance-notes
e8fd48025d..5cc10d4786 refs/notes/perf -> refs/notes/perf
$ mkdir -p public/doc
$ tar -xf haddock.html.tar.xz -C public/doc
tar: haddock.html.tar.xz: Cannot open: No such file or directory
tar: Error is not recoverable: exiting now
ERROR: Job failed: exit code 1