Run pdflatex three times during PDF build

We had a report in #1557 that creating the index for the PDF does not work and
that it might be related to how often we run `pdflatex` during the build.

Related #1557.

readthedocs/doc_builder/backends/sphinx.py

@@ -287,6 +287,10 @@ def build(self, **kwargs):
  cmd_ret = self.build_env.run_command_class(
  cls=LatexBuildCommand, cmd=cmd, cwd=latex_cwd, warn_only=True)
  pdf_commands.append(cmd_ret)
+ for cmd in pdflatex_cmds:
+ cmd_ret = self.build_env.run_command_class(
+ cls=LatexBuildCommand, cmd=cmd, cwd=latex_cwd, warn_only=True)
+ pdf_commands.append(cmd_ret)
  for cmd in pdflatex_cmds:
  cmd_ret = self.build_env.run_command_class(
  cls=LatexBuildCommand, cmd=cmd, cwd=latex_cwd, warn_only=True)