[clang] [WebAssembly] Enable Wasm EH features only once (PR #124042)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-aarch64-quick` running on `linaro-clang-aarch64-quick` while building `clang` at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/65/builds/11149

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

```
Step 5 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'LLVM-Unit :: Support/./SupportTests/130/174' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:/home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/unittests/Support/./SupportTests-LLVM-Unit-3334394-130-174.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=174 GTEST_SHARD_INDEX=130 /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/unittests/Support/./SupportTests
--

Script:
--
/home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/unittests/Support/./SupportTests --gtest_filter=ProgramEnvTest.TestLockFile
--
Note: Google Test filter = ProgramEnvTest.TestLockFile
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from ProgramEnvTest
../llvm/llvm/unittests/Support/ProgramTest.cpp:558: Failure
Value of: Error.empty()
  Actual: false
Expected: true


../llvm/llvm/unittests/Support/ProgramTest.cpp:558
Value of: Error.empty()
  Actual: false
Expected: true



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


```

</details>

https://github.com/llvm/llvm-project/pull/124042