Help: Fix broken cross-references reported by 'nitpicky' option

Enable the Sphinx 'nitpicky' option and fix the resulting warnings about
dangling references.

Help/command/target_compile_options.rst

@@ -12,8 +12,8 @@ Add compile options to a target.
 Specify compile options to use when compiling a given target.  The
 named ``<target>`` must have been created by a command such as
 :command:`add_executable` or :command:`add_library` and must not be an
-:prop_tgt:`IMPORTED Target`.  If ``BEFORE`` is specified, the content will
-be prepended to the property instead of being appended.
+:ref:`IMPORTED Target <Imported Targets>`.  If ``BEFORE`` is specified,
+the content will be prepended to the property instead of being appended.
 
 This command can be used to add any options, but
 alternative commands exist to add preprocessor definitions

Help/command/target_sources.rst

@@ -12,7 +12,7 @@ Add sources to a target.
 Specify sources to use when compiling a given target.  The
 named ``<target>`` must have been created by a command such as
 :command:`add_executable` or :command:`add_library` and must not be an
-:prop_tgt:`IMPORTED Target`.
+:ref:`IMPORTED Target <Imported Targets>`.
 
 The ``INTERFACE``, ``PUBLIC`` and ``PRIVATE`` keywords are required to
 specify the scope of the following arguments.  ``PRIVATE`` and ``PUBLIC``

Help/prop_sf/AUTOUIC_OPTIONS.rst

@@ -6,7 +6,7 @@ Additional options for ``uic`` when using :prop_tgt:`AUTOUIC`
 This property holds additional command line options
 which will be used when ``uic`` is executed during the build via :prop_tgt:`AUTOUIC`,
 i.e. it is equivalent to the optional ``OPTIONS`` argument of the
-:module:`qt4_wrap_ui()<FindQt4>` macro.
+:module:`qt4_wrap_ui() <FindQt4>` macro.
 
 By default it is empty.