.shippable: --disable-docs for cross-compile tests

The sphinx support is fairly new and we don't seem to have all the
bugs worked out for cross development environments right now.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200203090932.19147-6-alex.bennee@linaro.org>

.shippable.yml

@@ -37,5 +37,5 @@ build:
     - unset CC
     - mkdir build
     - cd build
-    - ../configure ${QEMU_CONFIGURE_OPTS} --target-list=${TARGET_LIST}
+    - ../configure --disable-docs ${QEMU_CONFIGURE_OPTS} --target-list=${TARGET_LIST}
     - make -j$(($(getconf _NPROCESSORS_ONLN) + 1))