[lld] [ELF] Support R_RISCV_SET_ULEB128/R_RISCV_SUB_ULEB128 in SHF_ALLOC sections (PR #77261)

[Fangrui Song via llvm-commits]

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@@ -122,8 +167,21 @@ w1: call foo; w2:
 
 #--- overflow.s
 w1: call foo; w2:
+.section .alloc,"a"
+.quad 0
+.reloc ., R_RISCV_SET_ULEB128, w2+124
+.reloc ., R_RISCV_SUB_ULEB128, w1
+.byte 0x7f
 .section .debug_rnglists
 .quad 0
 .reloc ., R_RISCV_SET_ULEB128, w2+124
 .reloc ., R_RISCV_SUB_ULEB128, w1
 .byte 0x7f
+
+#--- preemptable.s
+.globl w1, w2
----------------
MaskRay wrote:

In the future, I'll consider making `R_RISCV_ADD` a constant only if `!isPreemptible` like `R_RISCV_LEB128`

https://github.com/llvm/llvm-project/pull/77261