[clang] [llvm] [Clang][AMDGPU] Get correct nullptr value for AS3 and AS5 (PR #175610)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-sie-ubuntu-fast` running on `sie-linux-worker` while building `clang,llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/144/builds/43913

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'Clang :: CodeGen/AMDGPU/nullptr-in-different-address-spaces.cpp' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 2
/home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/clang -cc1 -internal-isystem /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/lib/clang/22/include -nostdsysteminc -triple amdgcn-amd-amdhsa -target-cpu gfx900 -O1 -emit-llvm -o - /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang/test/CodeGen/AMDGPU/nullptr-in-different-address-spaces.cpp | /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/FileCheck /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang/test/CodeGen/AMDGPU/nullptr-in-different-address-spaces.cpp
# executed command: /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/clang -cc1 -internal-isystem /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/lib/clang/22/include -nostdsysteminc -triple amdgcn-amd-amdhsa -target-cpu gfx900 -O1 -emit-llvm -o - /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang/test/CodeGen/AMDGPU/nullptr-in-different-address-spaces.cpp
# note: command had no output on stdout or stderr
# executed command: /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/FileCheck /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang/test/CodeGen/AMDGPU/nullptr-in-different-address-spaces.cpp
# .---command stderr------------
# | /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang/test/CodeGen/AMDGPU/nullptr-in-different-address-spaces.cpp:10:16: error: CHECK-NEXT: expected string not found in input
# | // CHECK-NEXT: [[TMP0:%.*]] = load ptr addrspace(3), ptr addrspace(1) @ptr_as3, align 4
# |                ^
# | <stdin>:11:7: note: scanning from here
# | entry:
# |       ^
# | <stdin>:12:25: note: possible intended match here
# |  %0 = load ptr addrspace(3), ptr addrspacecast (ptr addrspace(1) @ptr_as3 to ptr), align 4
# |                         ^
# | /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang/test/CodeGen/AMDGPU/nullptr-in-different-address-spaces.cpp:22:16: error: CHECK-NEXT: expected string not found in input
# | // CHECK-NEXT: [[TMP0:%.*]] = load ptr addrspace(3), ptr addrspace(1) @ptr_as3, align 4
# |                ^
# | <stdin>:20:7: note: scanning from here
# | entry:
# |       ^
# | <stdin>:21:25: note: possible intended match here
# |  %0 = load ptr addrspace(3), ptr addrspacecast (ptr addrspace(1) @ptr_as3 to ptr), align 4
# |                         ^
# | /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang/test/CodeGen/AMDGPU/nullptr-in-different-address-spaces.cpp:35:16: error: CHECK-NEXT: expected string not found in input
# | // CHECK-NEXT: [[TMP0:%.*]] = load ptr addrspace(5), ptr addrspace(1) @ptr_as5, align 4
# |                ^
# | <stdin>:29:7: note: scanning from here
# | entry:
# |       ^
# | <stdin>:30:25: note: possible intended match here
# |  %0 = load ptr addrspace(5), ptr addrspacecast (ptr addrspace(1) @ptr_as5 to ptr), align 4
# |                         ^
# | /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang/test/CodeGen/AMDGPU/nullptr-in-different-address-spaces.cpp:47:16: error: CHECK-NEXT: expected string not found in input
# | // CHECK-NEXT: [[TMP0:%.*]] = load ptr addrspace(5), ptr addrspace(1) @ptr_as5, align 4
# |                ^
# | <stdin>:38:7: note: scanning from here
# | entry:
# |       ^
# | <stdin>:39:25: note: possible intended match here
# |  %0 = load ptr addrspace(5), ptr addrspacecast (ptr addrspace(1) @ptr_as5 to ptr), align 4
# |                         ^
# | 
# | Input file: <stdin>
# | Check file: /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/clang/test/CodeGen/AMDGPU/nullptr-in-different-address-spaces.cpp
...

```

</details>

https://github.com/llvm/llvm-project/pull/175610