libstdc++: Fix Doxygen warnings

libstdc++-v3/ChangeLog:

	* include/bits/alloc_traits.h: Use markdown for code font.
	* include/bits/basic_string.h: Fix @param names.
	* include/bits/max_size_type.h: Remove period after @file.
	* include/bits/regex.h: Fix duplicate @retval names, and rename.
	* include/ext/pb_ds/detail/priority_queue_base_dispatch.hpp: Add
	group open to match existing group close.
	* include/ext/pb_ds/priority_queue.hpp: Add blank line before group
	open.

libstdc++-v3/include/bits/alloc_traits.h

@@ -341,7 +341,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       { __a.deallocate(__p, __n); }
 
       /**
-       *  @brief  Construct an object of type @a _Tp
+       *  @brief  Construct an object of type `_Tp`
        *  @param  __a  An allocator.
        *  @param  __p  Pointer to memory of suitable size and alignment for Tp
        *  @param  __args Constructor arguments.

libstdc++-v3/include/bits/basic_string.h

@@ -4707,9 +4707,9 @@ _GLIBCXX_END_NAMESPACE_CXX11
 
       /**
        *  @brief  Insert a string_view.
-       *  @param __pos  Position in string to insert at.
-       *  @param __svt  The object convertible to string_view to insert from.
-       *  @param __pos  Position in string_view to insert
+       *  @param __pos1  Position in string to insert at.
+       *  @param __svt   The object convertible to string_view to insert from.
+       *  @param __pos2  Position in string_view to insert
        *  from.
        *  @param __n    The number of characters to insert.
        *  @return  Reference to this string.

libstdc++-v3/include/bits/max_size_type.h

@@ -22,7 +22,7 @@
 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 // <http://www.gnu.org/licenses/>.
 
-/** @file bits/max_size_type.h.
+/** @file bits/max_size_type.h
  *  This is an internal header file, included by other library headers.
  *  Do not attempt to use it directly. @headername{iterator}
  */

libstdc++-v3/include/bits/regex.h

@@ -916,9 +916,9 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *
        * @param __s Another matched sequence to compare to this one.
        *
-       * @retval <0 this matched sequence will collate before @p __s.
-       * @retval =0 this matched sequence is equivalent to @p __s.
-       * @retval <0 this matched sequence will collate after @p __s.
+       * @retval negative  This matched sequence will collate before `__s`.
+       * @retval zero      This matched sequence is equivalent to `__s`.
+       * @retval positive  This matched sequence will collate after `__s`.
        */
       int
       compare(const sub_match& __s) const
@@ -926,13 +926,13 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 
       /**
        * @{
-       * @brief Compares this sub_match to a string.
+       * @brief Compares this `sub_match` to a string.
        *
-       * @param __s A string to compare to this sub_match.
+       * @param __s A string to compare to this `sub_match`.
        *
-       * @retval <0 this matched sequence will collate before @p __s.
-       * @retval =0 this matched sequence is equivalent to @p __s.
-       * @retval <0 this matched sequence will collate after @p __s.
+       * @retval negative  This matched sequence will collate before `__s`.
+       * @retval zero      This matched sequence is equivalent to `__s`.
+       * @retval positive  This matched sequence will collate after `__s`.
        */
       int
       compare(const string_type& __s) const

libstdc++-v3/include/ext/pb_ds/detail/priority_queue_base_dispatch.hpp

@@ -63,6 +63,12 @@ namespace __gnu_pbds
 {
   namespace detail
   {
+    /**
+     *  @ingroup pbds
+     *
+     *  @{
+     */
+
     /// Specialization for pairing_heap.
     template<typename _VTp, typename Cmp_Fn, typename _Alloc>
       struct container_base_dispatch<_VTp, Cmp_Fn, _Alloc, pairing_heap_tag,

libstdc++-v3/include/ext/pb_ds/priority_queue.hpp

@@ -51,6 +51,7 @@ namespace __gnu_pbds
   /**
    *  @defgroup heap-based Heap-Based
    *  @ingroup containers-pbds
+   *
    *  @{
    */
 
@@ -151,6 +152,6 @@ namespace __gnu_pbds
     swap(priority_queue& other)
     { base_type::swap(other); }
   };
-} // namespace __gnu_pbds
  ///@} heap-based
+} // namespace __gnu_pbds
 #endif