I haven't really had a chance to make a patch. But I've fixed this in my own fork, just add .getCallee() like this:

Function* pFunc = cast<Function>(JM()->mpCurrentModule->getOrInsertFunction("meta.intrinsic.VGATHERPD", pFuncTy).getCallee());

This is due to the fact that the functions now return an opaque pointer instead, wrapped in the FunctionCallee class, the offending commit is here:
https://github.com/llvm-mirror/llvm/commit/9ec60d7d8fa237f19210d325c8c058b89c7b17d2#diff-295d2c56655729b2bd6dc1dfca7c2f0e

The fix is needed several places, also in the codegen template

commit 93c81ca336f64c45e43f0c40cb5c5f9084745233
Author: Vinson Lee <vlee@freedesktop.org>
Date:   Mon Mar 18 11:52:48 2019 -0700

    swr: Fix build with llvm-9.0.
    
    Fix build error after llvm-9.0svn r352827 ("[opaque pointer types] Add a
    FunctionCallee wrapper type, and use it.").
    
    In file included from ./rasterizer/jitter/builder.h:158:0,
                     from swr_shader.cpp:35:
    ./rasterizer/jitter/gen_builder_meta.hpp: In member function ‘llvm::Value* SwrJit::Builder::VGATHERPD(llvm::Value*, 
llvm::Value*, llvm::Value*, llvm::Value*, llvm::Value*, const llvm:
    :Twine&)’:
    ./rasterizer/jitter/gen_builder_meta.hpp:51:117: error: no matching function for call to ‘cast(llvm::FunctionCallee)
’
         Function* pFunc = cast<Function>(JM()->mpCurrentModule->getOrInsertFunction("meta.intrinsic.VGATHERPD", pFuncTy));
                                                                                                                         ^
    
    Suggested-by: Philip Meulengracht <the_meulengracht@hotmail.com>
    Signed-off-by: Vinson Lee <vlee@freedesktop.org>
    Reviewed-by: Alok Hota <alok.hota@intel.com>