[rtsan][llvm][NFC] Rename sanitize_realtime_unsafe attr to sanitize_realtime_blocking (#113155)

# What

This PR renames the newly-introduced llvm attribute
`sanitize_realtime_unsafe` to `sanitize_realtime_blocking`. Likewise,
sibling variables such as `SanitizeRealtimeUnsafe` are renamed to
`SanitizeRealtimeBlocking` respectively. There are no other functional
changes.


# Why?

- There are a number of problems that can cause a function to be
real-time "unsafe",
- we wish to communicate what problems rtsan detects and *why* they're
unsafe, and
- a generic "unsafe" attribute is, in our opinion, too broad a net -
which may lead to future implementations that need extra contextual
information passed through them in order to communicate meaningful
reasons to users.
- We want to avoid this situation and make the runtime library boundary
API/ABI as simple as possible, and
- we believe that restricting the scope of attributes to names like
`sanitize_realtime_blocking` is an effective means of doing so.

We also feel that the symmetry between `[[clang::blocking]]` and
`sanitize_realtime_blocking` is easier to follow as a developer.

# Concerns

- I'm aware that the LLVM attribute `sanitize_realtime_unsafe` has been
part of the tree for a few weeks now (introduced here:
https://github.com/llvm/llvm-project/pull/106754). Given that it hasn't
been released in version 20 yet, am I correct in considering this to not
be a breaking change?

1 files changed, 2 insertions, 2 deletions

diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
index d900214..ee9cc4b 100644
--- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -853,8 +853,8 @@ static uint64_t getAttrKindEncoding(Attribute::AttrKind Kind) {
     return bitc::ATTR_KIND_SANITIZE_NUMERICAL_STABILITY;
   case Attribute::SanitizeRealtime:
     return bitc::ATTR_KIND_SANITIZE_REALTIME;
-  case Attribute::SanitizeRealtimeUnsafe:
-    return bitc::ATTR_KIND_SANITIZE_REALTIME_UNSAFE;
+  case Attribute::SanitizeRealtimeBlocking:
+    return bitc::ATTR_KIND_SANITIZE_REALTIME_BLOCKING;
   case Attribute::SpeculativeLoadHardening:
     return bitc::ATTR_KIND_SPECULATIVE_LOAD_HARDENING;
   case Attribute::SwiftError: