Update the LangRef to reflect reality.

At the very least, we have CallInst::setIsNoInline() for adding the
noinline attribute to callsites, and I'm told alwaysinline seems to
work.

Thought of adding "not all attributes are guaranteed to work here". If
someone thinks that would be better (or has a better way of phrasing
that, etc.), happy to add it.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@300168 91177308-0d34-0410-b5e6-96231b3b80d8

docs/LangRef.rst

@@ -8873,9 +8873,7 @@ This instruction requires several arguments:
    be of :ref:`first class <t_firstclass>` type. If the function signature
    indicates the function accepts a variable number of arguments, the
    extra arguments can be specified.
-#. The optional :ref:`function attributes <fnattrs>` list. Only
-   '``noreturn``', '``nounwind``', '``readonly``' , '``readnone``',
-   and '``convergent``' attributes are valid here.
+#. The optional :ref:`function attributes <fnattrs>` list.
 #. The optional :ref:`operand bundles <opbundles>` list.
 
 Semantics: