[clang] [flang] [flang][Driver] Enable bare -O flag alias for flang (PR #228483)

[Tarun Prabhu via cfe-commits]

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@@ -0,0 +1,34 @@
+! Test that -O flags are correctly forwarded as -plugin-opt=O<n> to the linker
+! when LTO is enabled.
+
+! UNSUPPORTED: system-windows, system-solaris
+
+! --- Linux / lld ---
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tarunprabhu wrote:

Are we intentionally testing Linux + lld here? If this is only testing that the command lines are enabled correctly, it may be better, as in the AIX case, to just use the default linker to keep the test simple.

https://github.com/llvm/llvm-project/pull/228483