[clang] [llvm] Enable fexec-charset option (PR #138895)

[Richard Smith via llvm-commits]

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@@ -243,10 +243,11 @@
 // RUN: not %clang_cl /source-charset:utf-16 -### -- %s 2>&1 | FileCheck -check-prefix=source-charset-utf-16 %s
 // source-charset-utf-16: invalid value 'utf-16' in '/source-charset:utf-16'
 
-// /execution-charset: should warn on everything except UTF-8.
-// RUN: not %clang_cl /execution-charset:utf-16 -### -- %s 2>&1 | FileCheck -check-prefix=execution-charset-utf-16 %s
-// execution-charset-utf-16: invalid value 'utf-16' in '/execution-charset:utf-16'
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zygoloid wrote:

What happens for the old example of `/execution-charset:utf-16` / `-fexec-charset=utf-16`? Presumably that should also be an error, because we're setting the *narrow* execution character set here and it doesn't make sense to set that to a non-narrow encoding such as UTF-16 or UCS-4.

https://github.com/llvm/llvm-project/pull/138895