[llvm] [bazel] Revert "[bazel] llvm-config.h: Turn on LLVM_ENABLE_PLUGINS" as it fails TensorFlow Windows build (PR #143419)

[NAKAMURA Takumi via llvm-commits]

chapuni wrote:

@rnk For now, I made a change enable PLUGINS only on posix.
Regarding to llvm/CMakeLists.txt, PLUGINS is turned off by default for targeting Windows ABI.

Excuse me, I misunderstood the log above as cl.exe at a glance.

https://github.com/llvm/llvm-project/pull/143419