GCN: fix_alloca_addrspace doesn't handle nested pointers

```
julia-debug: /home/tim/Julia/src/julia/deps/srccache/llvm-julia-13.0.1-0/llvm/lib/IR/Value.cpp:493: void llvm::Value::doRAUW(llvm::Value*, llvm::Value::ReplaceMetadataUses): Assertion `New->getType() == getType() && "replaceAllUses of value with new value of different type!"' failed.
```

```
#0 0x00007ffff7e1c34c in __pthread_kill_implementation () from /usr/lib/libc.so.6
#1 0x00007ffff7dcf4b8 in raise () from /usr/lib/libc.so.6
#2 0x00007ffff7db9534 in abort () from /usr/lib/libc.so.6
#3 0x00007ffff7db945c in __assert_fail_base.cold () from /usr/lib/libc.so.6
#4 0x00007ffff7dc8116 in __assert_fail () from /usr/lib/libc.so.6
#5 0x00007fffee7b2a09 in llvm::Value::doRAUW (this=0x5555577e2400, New=0x555556ae39d0, ReplaceMetaUses=llvm::Value::ReplaceMetadataUses::Yes)
at /home/tim/Julia/src/julia/deps/srccache/llvm-julia-13.0.1-0/llvm/lib/IR/Value.cpp:493
#6 0x00007fffee7b2b62 in llvm::Value::replaceAllUsesWith (this=0x5555577e2400, New=0x555556ae39d0) at /home/tim/Julia/src/julia/deps/srccache/llvm-julia-13.0.1-0/llvm/lib/IR/Value.cpp:521
#7 0x00007fffef69d1e7 in llvm::BitcodeReaderValueList::assignValue (this=0x5555580eb728, V=0x555556ae39d0, Idx=67)
at /home/tim/Julia/src/julia/deps/srccache/llvm-julia-13.0.1-0/llvm/lib/Bitcode/Reader/ValueList.cpp:88
#8 0x00007fffef6432ec in (anonymous namespace)::BitcodeReader::parseFunctionBody (this=0x5555580eb4e0, F=0x555555eab788)
at /home/tim/Julia/src/julia/deps/srccache/llvm-julia-13.0.1-0/llvm/lib/Bitcode/Reader/BitcodeReader.cpp:5415
#9 0x00007fffef643b4d in (anonymous namespace)::BitcodeReader::materialize (this=0x5555580eb4e0, GV=0x555555eab788)
at /home/tim/Julia/src/julia/deps/srccache/llvm-julia-13.0.1-0/llvm/lib/Bitcode/Reader/BitcodeReader.cpp:5499
#10 0x00007fffef64456a in (anonymous namespace)::BitcodeReader::materializeModule (this=0x5555580eb4e0)
at /home/tim/Julia/src/julia/deps/srccache/llvm-julia-13.0.1-0/llvm/lib/Bitcode/Reader/BitcodeReader.cpp:5598
#11 0x00007fffee72a4cb in llvm::Module::materializeAll (this=0x555557547880) at /home/tim/Julia/src/julia/deps/srccache/llvm-julia-13.0.1-0/llvm/lib/IR/Module.cpp:453
#12 0x00007fffef64b90e in llvm::BitcodeModule::getModuleImpl(llvm::LLVMContext&, bool, bool, bool, llvm::function_ref, std::allocator > > (llvm::StringRef)>) (this=0x7fffffff1de0, Context=..., MaterializeAll=true, ShouldLazyLoadMetadata=false, IsImporting=false, DataLayoutCallback=...)
at /home/tim/Julia/src/julia/deps/srccache/llvm-julia-13.0.1-0/llvm/lib/Bitcode/Reader/BitcodeReader.cpp:6795
#13 0x00007fffef64cdeb in llvm::BitcodeModule::parseModule(llvm::LLVMContext&, llvm::function_ref, std::allocator > > (llvm::StringRef)>) (this=0x7fffffff1de0, Context=..., DataLayoutCallback=...) at /home/tim/Julia/src/julia/deps/srccache/llvm-julia-13.0.1-0/llvm/lib/Bitcode/Reader/BitcodeReader.cpp:6977
#14 0x00007fffef64cebd in llvm::parseBitcodeFile(llvm::MemoryBufferRef, llvm::LLVMContext&, llvm::function_ref, std::allocator > > (llvm::StringRef)>) (Buffer=..., Context=..., DataLayoutCallback=...) at /home/tim/Julia/src/julia/deps/srccache/llvm-julia-13.0.1-0/llvm/lib/Bitcode/Reader/BitcodeReader.cpp:6989
#15 0x00007fffef623b3b in LLVMParseBitcodeInContext2 (ContextRef=0x55555559c1d0, MemBuf=0x555556ae3880, OutModule=0x7fffffff1f10)
at /home/tim/Julia/src/julia/deps/srccache/llvm-julia-13.0.1-0/llvm/lib/Bitcode/Reader/BitReader.cpp:65
#16 0x00007fff703385a2 in LLVMParseBitcodeInContext2 () at /home/tim/Julia/depot/packages/LLVM/tVv0H/lib/13/libLLVM_h.jl:5863
#17 julia_#parse#80_701 (ctx=..., membuf=...) at /home/tim/Julia/depot/packages/LLVM/tVv0H/src/bitcode.jl:6
#18 0x00007fff7035cbdc in parse##kw () at /home/tim/Julia/depot/packages/LLVM/tVv0H/src/bitcode.jl:4
#19 #parse#81 () at /home/tim/Julia/depot/packages/LLVM/tVv0H/src/bitcode.jl:12
#20 parse##kw () at /home/tim/Julia/depot/packages/LLVM/tVv0H/src/bitcode.jl:12
#21 #97 () at /home/tim/Julia/pkg/GPUCompiler/src/rtlib.jl:168
#22 julia_#open#377_1037 (kwargs=..., f=..., args...=...) at io.jl:384
#23 0x00007fff7035d352 in open () at io.jl:382
#24 julia_#95_1029 () at /home/tim/Julia/pkg/GPUCompiler/src/rtlib.jl:167
#25 0x00007fff7035ea3f in julia_lock_1026 (f=..., l=...) at lock.jl:185
#26 0x00007fff7035eb32 in jfptr_lock_1027 ()
#27 0x00007ffff736296a in _jl_invoke (F=0x7fffdcddcdc0 , args=0x7fffffff2e28, nargs=2, mfunc=0x7ffd8b6e83d0, world=32392) at /home/tim/Julia/src/julia/src/gf.c:2339
#28 0x00007ffff736340c in ijl_apply_generic (F=0x7fffdcddcdc0 , args=0x7fffffff2e28, nargs=2) at /home/tim/Julia/src/julia/src/gf.c:2540
#29 0x00007fff70335d7e in julia_#load_runtime#94_741 (ctx=..., job=0x0) at /home/tim/Julia/pkg/GPUCompiler/src/utils.jl:64
#30 0x00007fff7033c290 in load_runtime##kw () at /home/tim/Julia/pkg/GPUCompiler/src/utils.jl:62
```

```
#5 0x00007fffee7b2a09 in llvm::Value::doRAUW (this=0x5555577e2400, New=0x555556ae39d0, ReplaceMetaUses=llvm::Value::ReplaceMetadataUses::Yes)
at /home/tim/Julia/src/julia/deps/srccache/llvm-julia-13.0.1-0/llvm/lib/IR/Value.cpp:493
493 assert(New->getType() == getType() &&

(gdb) call getType()->dump()
{} addrspace(10)**
(gdb) call New->getType()->dump()
{} addrspace(10)* addrspace(5)*

(gdb) up

(gdb) call F->dump()
; Materializable
define i64 @ijl_unbox_uint64({} addrspace(10)* nonnull readonly %0) local_unnamed_addr #0 {
%2 = alloca {} addrspace(10)*, align 8, addrspace(5)
}
```