[llvm] [JITLink][i386] Avoid 'i386' name clashing with built-in macro (PR #137063)

[Jessica Clarke via llvm-commits]

jrtc27 wrote:

> When compiling llvm on an actual i386 platform, both clang and gcc define a built-in macro `i386` to the value 1.

\* As GNU C/C++. This of course also extends to any third-party code that includes this header.

https://github.com/llvm/llvm-project/pull/137063