[compiler-rt] [compiler-rt][sanitizer] fix i386 build for Haiku (PR #171075)

[Jérôme Duval via llvm-commits]

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@@ -1987,7 +1987,7 @@ SignalContext::WriteFlag SignalContext::GetWriteFlag() const {
 #    elif SANITIZER_NETBSD
   uptr err = ucontext->uc_mcontext.__gregs[_REG_ERR];
 #    elif SANITIZER_HAIKU
-  uptr err = ucontext->uc_mcontext.r13;
+  uptr err = 0;  // ucontext->uc_mcontext.r13;
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korli wrote:

The err register got added on the main branch, but isn't yet on the current Haiku release. See https://github.com/haiku/haiku/commit/11adda21aa4e6b24f71a496868a44d7607bc3764 for more info. We'll use the register when possible.

https://github.com/llvm/llvm-project/pull/171075