[llvm] [LLVM] Remove 'LLVM_LIBC_GPU_BUILD' logic (PR #211265)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-ppc64le-linux-test-suite` running on `ppc64le-clang-test-suite` while building `llvm,offload` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/95/builds/21769

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

```
Step 6 (test-build-unified-tree-check-all) failure: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
...
PASS: UBSan-AddressSanitizer-powerpc64le :: TestCases/ImplicitConversion/signed-integer-truncation-ignorelist.c (113339 of 113350)
PASS: ThreadSanitizer-powerpc64le :: restore_stack.cpp (113340 of 113350)
PASS: ScudoStandalone-Unit :: ./ScudoUnitTest-powerpc64le-Test/117/375 (113341 of 113350)
PASS: ScudoStandalone-Unit :: ./ScudoUnitTest-powerpc64le-Test/21/375 (113342 of 113350)
PASS: ScudoStandalone-Unit :: ./ScudoUnitTest-powerpc64le-Test/102/375 (113343 of 113350)
PASS: ScudoStandalone-Unit :: ./ScudoUnitTest-powerpc64le-Test/101/375 (113344 of 113350)
PASS: ScudoStandalone-Unit :: ./ScudoCxxUnitTest-powerpc64le-Test/0/3 (113345 of 113350)
PASS: ScudoStandalone-Unit :: ./ScudoUnitTest-powerpc64le-Test/105/375 (113346 of 113350)
PASS: ScudoStandalone-Unit :: ./ScudoUnitTest-powerpc64le-Test/107/375 (113347 of 113350)
PASS: ScudoStandalone-Unit :: ./ScudoUnitTest-powerpc64le-Test/104/375 (113348 of 113350)
command timed out: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=20372.351818

```

</details>

https://github.com/llvm/llvm-project/pull/211265