riscv: link libgcc for jemalloc's __ffsdi2

[kali]

Base rv64gc has no count-trailing-zeros instruction, so gcc lowers the ffs in bit_util.h to a __ffsdi2 libgcc call. rust's compiler_builtins ships the rest of the *di2 family but not that one, so linking a static riscv64 binary fails with undefined reference to `__ffsdi2'.

Name libgcc for riscv as is already done for android, guarded on a gnu-like compiler so a clang/compiler-rt toolchain is left alone.

Summary by CodeRabbit

• Bug Fixes
  • Improved builds for RISC-V targets using GNU-like compilers by ensuring the required compiler support library is linked.
  • Resolved linker failures on base RV64GC systems lacking the Zbb extension.

[ti-chi-bot]

Welcome @kali! It looks like this is your first PR to tikv/jemallocator 🎉

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Team

Run ID: 1828cedd-21f9-486d-89a9-9feebbad9df2

📥 Commits

Reviewing files that changed from the base of the PR and between 0e91291 and 3db58f2.

📒 Files selected for processing (1)

• jemalloc-sys/build.rs

Included review availability: Your plan provides up to 4 included reviews per hour; 3 remain after this review.

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📝 Walkthrough

Walkthrough

The RISC-V build script now links gcc when it detects a GNU-like compiler. This supplies __ffsdi2 for rv64gc builds while retaining the existing atomic linkage.

Changes

RISC-V linker configuration

Layer / File(s)	Summary
GNU libgcc linkage jemalloc-sys/build.rs	The RISC-V branch checks compiler.is_like_gnu() and links gcc when the condition is true.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Merge Risk: ⚪ Minimal · up to 3db58

GNU RISC-V builds now link libgcc to resolve the missing __ffsdi2 symbol for base rv64gc targets, without changing Clang/compiler-rt linkage. No current merge-blocking risk is identified.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: linking libgcc for jemalloc's RISC-V __ffsdi2 dependency.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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