Fix generation of documentation for UndefinedBehaviorSanitizer.

[etienneb]

Summary

The text is mis-aligned.

[etienneb]

This got fixed.
Abandoning this change.

docs/UndefinedBehaviorSanitizer.rst

Available checks are:
   -  ``-fsanitize=function``: Indirect call of a function through a
      function pointer of the wrong type (Linux, C++ and x86/x86_64 only).
   -  ``-fsanitize=integer-divide-by-zero``: Integer division by zero.
   -  ``-fsanitize=nonnull-attribute``: Passing null pointer as a function
      parameter which is declared to never be null.
   -  ``-fsanitize=null``: Use of a null pointer or creation of a null
      reference.
   -  ``-fsanitize=object-size``: An attempt to potentially use bytes which
      the optimizer can determine are not part of the object being accessed.
      This will also detect some types of undefined behavior that may not
      directly access memory, but are provably incorrect given the size of
      the objects involved, such as invalid downcasts and calling methods on
      invalid pointers. These checks are made in terms of
      ``__builtin_object_size``, and consequently may be able to detect more
      problems at higher optimization levels.
   -  ``-fsanitize=return``: In C++, reaching the end of a
      value-returning function without returning a value.
   -  ``-fsanitize=returns-nonnull-attribute``: Returning null pointer
      from a function which is declared to never return null.
   -  ``-fsanitize=shift``: Shift operators where the amount shifted is
      greater or equal to the promoted bit-width of the left hand side
      or less than zero, or where the left hand side is negative. For a
      signed left shift, also checks for signed overflow in C, and for