Change llvmcall docs binding

The docstring for `llvmcall` was bound to a keyword rather than
the actual intrinsic `Core.Intrinsics.llvmcall`.

This produced the following odd behaviour when trying to find the docs:

    help?> llvmcall

    ... docs ...

    julia> llvmcall
    ERROR: UndefVarError: llvmcall not defined

    help?> Base.llvmcall

    ... no docs ...

    julia> Base.llvmcall
    (intrinsic function JuliaLang#90)

base/docs/basedocs.jl

@@ -587,7 +587,7 @@ functions for further details). In most cases, this simply results in a call to
 
 See `test/llvmcall.jl` for usage examples.
 """
-kw"llvmcall"
+Core.Intrinsics.llvmcall
 
 """
 `begin...end` denotes a block of code.