[llvm] On Windows, in the release build script, fix detecting if clang-cl is in PATH (PR #149597)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `mlir-nvidia-gcc7` running on `mlir-nvidia` while building `llvm` at step 7 "test-build-check-mlir-build-only-check-mlir".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/116/builds/17152

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

```
Step 7 (test-build-check-mlir-build-only-check-mlir) failure: test (failure)
******************** TEST 'MLIR :: Integration/GPU/Vulkan/vector-deinterleave.mlir' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
/vol/worker/mlir-nvidia/mlir-nvidia-gcc7/llvm.obj/bin/mlir-opt /vol/worker/mlir-nvidia/mlir-nvidia-gcc7/llvm.src/mlir/test/Integration/GPU/Vulkan/vector-deinterleave.mlir -test-vulkan-runner-pipeline    | /vol/worker/mlir-nvidia/mlir-nvidia-gcc7/llvm.obj/bin/mlir-runner -      --shared-libs=/vol/worker/mlir-nvidia/mlir-nvidia-gcc7/llvm.obj/lib/libmlir_vulkan_runtime.so,/vol/worker/mlir-nvidia/mlir-nvidia-gcc7/llvm.obj/lib/libmlir_runner_utils.so      --entry-point-result=void | /vol/worker/mlir-nvidia/mlir-nvidia-gcc7/llvm.obj/bin/FileCheck /vol/worker/mlir-nvidia/mlir-nvidia-gcc7/llvm.src/mlir/test/Integration/GPU/Vulkan/vector-deinterleave.mlir
# executed command: /vol/worker/mlir-nvidia/mlir-nvidia-gcc7/llvm.obj/bin/mlir-opt /vol/worker/mlir-nvidia/mlir-nvidia-gcc7/llvm.src/mlir/test/Integration/GPU/Vulkan/vector-deinterleave.mlir -test-vulkan-runner-pipeline
# executed command: /vol/worker/mlir-nvidia/mlir-nvidia-gcc7/llvm.obj/bin/mlir-runner - --shared-libs=/vol/worker/mlir-nvidia/mlir-nvidia-gcc7/llvm.obj/lib/libmlir_vulkan_runtime.so,/vol/worker/mlir-nvidia/mlir-nvidia-gcc7/llvm.obj/lib/libmlir_runner_utils.so --entry-point-result=void
# .---command stderr------------
# |  failed with error code 0 when executing vkCreateDevicerunOnVulkan failed
# `-----------------------------
# executed command: /vol/worker/mlir-nvidia/mlir-nvidia-gcc7/llvm.obj/bin/FileCheck /vol/worker/mlir-nvidia/mlir-nvidia-gcc7/llvm.src/mlir/test/Integration/GPU/Vulkan/vector-deinterleave.mlir
# .---command stderr------------
# | /vol/worker/mlir-nvidia/mlir-nvidia-gcc7/llvm.src/mlir/test/Integration/GPU/Vulkan/vector-deinterleave.mlir:6:11: error: CHECK: expected string not found in input
# | // CHECK: [0, 2]
# |           ^
# | <stdin>:1:1: note: scanning from here
# | Unranked Memref base@ = 0x5cbfed9f0820 rank = 1 offset = 0 sizes = [2] strides = [1] data = 
# | ^
# | <stdin>:2:1: note: possible intended match here
# | [0, 0]
# | ^
# | 
# | Input file: <stdin>
# | Check file: /vol/worker/mlir-nvidia/mlir-nvidia-gcc7/llvm.src/mlir/test/Integration/GPU/Vulkan/vector-deinterleave.mlir
# | 
# | -dump-input=help explains the following input dump.
# | 
# | Input was:
# | <<<<<<
# |            1: Unranked Memref base@ = 0x5cbfed9f0820 rank = 1 offset = 0 sizes = [2] strides = [1] data =  
# | check:6'0     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
# |            2: [0, 0] 
# | check:6'0     ~~~~~~~
# | check:6'1     ?       possible intended match
# |            3: Unranked Memref base@ = 0x5cbfeda30a20 rank = 1 offset = 0 sizes = [2] strides = [1] data =  
# | check:6'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# |            4: [0, 0] 
# | check:6'0     ~~~~~~~
# | >>>>>>
# `-----------------------------
# error: command failed with exit status: 1

--

********************


```

</details>

https://github.com/llvm/llvm-project/pull/149597