[clang] [llvm] [RISCV] Add B extension (PR #76893)

[Pengcheng Wang via cfe-commits]

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@@ -920,8 +920,8 @@ void RISCVISAInfo::updateImplication() {
 }
 
 static constexpr StringLiteral CombineIntoExts[] = {
-    {"zk"},    {"zkn"},  {"zks"},   {"zvkn"},  {"zvknc"},
-    {"zvkng"}, {"zvks"}, {"zvksc"}, {"zvksg"},
+    {"b"},     {"zk"},    {"zkn"},  {"zks"},   {"zvkn"},
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wangpc-pp wrote:

> Remove this from `CombineIntoExts` may cause `__riscv_b` become less useful I think?

Yeah, but I think @topperc's concern makes sense as well. Will binutils complain or just ignore unknown extensions?

https://github.com/llvm/llvm-project/pull/76893