[llvm] [AArch64][SME] Use reportFatalUsageError rather than assert (NFC) (PR #145491)

[Mikael Holmén via llvm-commits]

================
@@ -0,0 +1,7 @@
+; RUN: not llc -mtriple aarch64-none-linux-gnu %s 2>&1 | FileCheck %s
----------------
mikaelholmen wrote:

Can we add "-o /dev/null" or something here to avoid opening an output file in the local directory, since it may be write protected?

https://github.com/llvm/llvm-project/pull/145491