clang-cl: Support MSVC2015's /validate-charset flag.
Clang always assumes that files are utf-8. If an invalidly encoded character is
used in an identifier, clang always errors. If it's used in a character
literal, clang warns Winvalid-source-encoding (on by default). Clang never
checks the encoding of things in comments (adding this seems like a nice
feature if it doesn't impact performance).
For cl.exe /utf-8 (which enables /validate-charset), if a bad character is used
in an identifier, it emits both an error and a warning. If it's used in a
literal or a comment, it emits a warning.
So mapping /validate-charset to -Winvalid-source-encoding seems like a fairly
decent fit.
https://reviews.llvm.org/D23945
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@279872
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