update llvmcall docs, opaque pointers are now supported (#59873)

(cherry picked from commit a0a65e6)

Author: simeonschaub

base/docs/basedocs.jl

@@ -1396,8 +1396,6 @@ a tuple of types. All types, as well as the LLVM code, should be specified as li
 not as variables or expressions (it may be necessary to use `@eval` to generate these
 literals).
 
-[Opaque pointers](https://llvm.org/docs/OpaquePointers.html) (written as `ptr`) are not allowed in the LLVM code.
-
 See
 [`test/llvmcall.jl`](https://github.com/JuliaLang/julia/blob/v$VERSION/test/llvmcall.jl)
 for usage examples.