[clang] Fix documentation on PGO/coverage related options. (PR #73845)

[Petr Hosek via cfe-commits]

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@@ -4401,13 +4413,18 @@ Execute ``clang-cl /?`` to see a list of supported options:
                               Instrument only functions from files where names don't match all the regexes separated by a semi-colon
       -fprofile-filter-files=<value>
                               Instrument only functions from files where names match any regex separated by a semi-colon
+      -fprofile-generate[=<dirname>]
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petrhosek wrote:

This is really surprising but I just tested this and you're correct. Do you know why that's the case, that is why `-fprofile-generate=<dirname>` and `-fprofile-instr-generate=<filename_pattern>` have a different behavior?

https://github.com/llvm/llvm-project/pull/73845