[llvm] Add target-byteorder for cases where endian in target triple is what matters (PR #107915)

[Eli Friedman via llvm-commits]

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@@ -1,5 +1,5 @@
 ; Avoid `!DL->isLittleEndian() && !CLI->enableBigEndian()` missmatch on PPC64BE.
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efriedma-quic wrote:

Really, what we want to check here is "does the target support globalisel", since we only want to check the behavior of `-global-isel=1` on such targets.  But the comment is basically correct; big-endian targets don't support globalisel (with the exception of m68k), so checking endianness is a reasonable approximation.

https://github.com/llvm/llvm-project/pull/107915