[clang][docs] Fix supported element types for `__builtin_reduce_(add|mul)`

[jloser]

Summary

The docs mention that __builtin_reduce_add and __builtin_reduce_mul support
both integer and floating point element types, but only integer element types
are actually supported. See https://github.com/llvm/llvm-project/issues/57847,
and specifically,
https://github.com/llvm/llvm-project/blob/00874c48ea4d291908517afaab50d1dcbfb016c3/clang/lib/Sema/SemaChecking.cpp#L2631 for the fact that floating point element types are not supported yet.

Fix the docs to only mention support for integer element types.

[nikic]

LG

[jloser]

This landed with https://github.com/llvm/llvm-project/commit/cf77333da986720e9aded4301d81a581e2be9611. The revision didn't auto-close for some reason.

[fhahn]

In D134316#3808544, @jloser wrote:

This landed with https://github.com/llvm/llvm-project/commit/cf77333da986720e9aded4301d81a581e2be9611. The revision didn't auto-close for some reason.

You need to make sure the commit message includes Differential Revision: https://reviews.llvm.org/D134316 for it to auto-close.

clang/docs/LanguageExtensions.rst

======================================= ================================================================ ==================================
          Name                            Operation                                                        Supported element types
 ======================================= ================================================================ ==================================
  ET __builtin_reduce_max(VT a)           return x or y, whichever is larger; If exactly one argument is   integer and floating point types
                                          a NaN, return the other argument. If both arguments are NaNs,
                                          fmax() return a NaN.
  ET __builtin_reduce_min(VT a)           return x or y, whichever is smaller; If exactly one argument     integer and floating point types
                                          is a NaN, return the other argument. If both arguments are
                                          NaNs, fmax() return a NaN.
- ET __builtin_reduce_add(VT a)           \+                                                               integer and floating point types
- ET __builtin_reduce_mul(VT a)           \*                                                               integer and floating point types
+ ET __builtin_reduce_add(VT a)           \+                                                               integer types
+ ET __builtin_reduce_mul(VT a)           \*                                                               integer types
  ET __builtin_reduce_and(VT a)           &                                                                integer types
  ET __builtin_reduce_or(VT a)            \|                                                               integer types
  ET __builtin_reduce_xor(VT a)           ^                                                                integer types
 ======================================= ================================================================ ==================================
 
 Matrix Types
 ============
 

 .. code-block:: c++
 
   #pragma clang attribute push (__declspec(dllexport), apply_to = function)
 
   void function(); // The function now has the __declspec(dllexport) attribute
 
   #pragma clang attribute pop
 
-A single push directive can contain multiple attributes, however, 
+A single push directive can contain multiple attributes, however,
 only one syntax style can be used within a single directive:
 
 .. code-block:: c++
 
   #pragma clang attribute push ([[noreturn, noinline]], apply_to = function)
 
   void function1(); // The function now has the [[noreturn]] and [[noinline]] attributes
 
   #pragma clang attribute pop
-  
   #pragma clang attribute push (__attribute((noreturn, noinline)), apply_to = function)
 
   void function2(); // The function now has the __attribute((noreturn)) and __attribute((noinline)) attributes
 
   #pragma clang attribute pop
 
 Because multiple push directives can be nested, if you're writing a macro that
 expands to ``_Pragma("clang attribute")`` it's good hygiene (though not