[clang] [profile] Add a clang option -fprofile-continuous that enables continuous instrumentation profiling mode (PR #124353)

[Fangrui Song via cfe-commits]

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+// 1) test on platforms that (do or do not) require runtime relocation
+//
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MaskRay wrote:

sed 's,^//$,,'

https://github.com/llvm/llvm-project/pull/124353