[clang] [llvm] [MC,llvm-readobj,yaml2obj] Support CREL relocation format (PR #91280)

[Fangrui Song via cfe-commits]

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@@ -86,6 +86,8 @@ DYNAMIC_TAG(RELRSZ, 35)  // Size of Relr relocation table.
 DYNAMIC_TAG(RELR, 36)    // Address of relocation table (Relr entries).
 DYNAMIC_TAG(RELRENT, 37) // Size of a Relr relocation entry.
 
+DYNAMIC_TAG(CREL,  38)   // CREL relocation table
+
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MaskRay wrote:

When I have more bandwidth to implement the DT_CREL support for binutils and some loader implementations, I'll use 38.
This avoids the potential annoyance of picking a version initially and then needing to change it later, which could cause issues with toolchain/loader interop inconvenience.

In practice, achieving consensus between major ELF toolchain vendors like GNU and LLVM is enough to prevent conflicts...
The generic ABI hasn't seen a new `DT_*` addition besides RELR since 2013.

https://github.com/llvm/llvm-project/pull/91280