[lld] [lld][ELF] Fix crash when relaxation pass encounters synthetic sections (PR #184758)

[Fangrui Song via llvm-commits]

================
@@ -0,0 +1,28 @@
+# REQUIRES: riscv
+# RUN: rm -rf %t && split-file %s %t
+# RUN: llvm-mc --filetype=obj -triple=riscv64 %t/a.s -o %t/a.o
----------------
MaskRay wrote:

Add `-mattr=+relax`

https://github.com/llvm/llvm-project/pull/184758