Fix HTML rendering of long-form options

We at present only have long-form options for configure, the scope
of the change is somewhat limited.  Our SmartyPants config for Sphinx
causes these options to appear as prefixed with an en dash, instead
of the two hyphens that demarcate the (GNU-style) long-form options.
Using a different type of markup for command options could work around
this, but that would be a much larger patch.
Instead, apply a workaround in the markup for display purposes, which
makes the source a bit more ugly but the output correct.
Man page output is unaffected.

This patch was automatically generated with:
git grep -- -- doc/rst_source | grep -v -- --- | cut -d ':' -f 1
 | uniq | xargs sed -i '' -e 's/\*\*--\([a-zA-Z]\)/**-**\\ **-\1/g'
and manually reviewed for correctness.

ticket: 7187

0 files changed, 0 insertions, 0 deletions