[llvm] [SystemZ][z/OS] Build in ASCII 64 bit mode on z/OS (PR #90630)

[via llvm-commits]

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@@ -1156,6 +1156,11 @@ if (CMAKE_SYSTEM_NAME MATCHES "OS390")
   add_compile_definitions(_OPEN_SYS_FILE_EXT) # Needed for EBCDIC I/O.
   add_compile_definitions(_EXT) # Needed for file data.
   add_compile_definitions(_UNIX03_THREADS) # Multithreading support.
+  # Need to build LLVM as ASCII application.
+  # This can't be a global setting because other projects may
+  # need to build in EBCDIC mode.
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zibi2 wrote:

```suggestion
  # need to be built in EBCDIC mode.
```

https://github.com/llvm/llvm-project/pull/90630