[Driver] Use libatomic for 32-bit SPARC atomics support on Linux

This is the Linux/sparc64 equivalent to D118021
<https://reviews.llvm.org/D118021>, necessary to provide an external
implementation of atomics on 32-bit SPARC which LLVM cannot inline even
with `-mcpu=v9` or an equivalent default.

Tested on `sparc64-unknown-linux-gnu`.

Differential Revision: https://reviews.llvm.org/D130569

(cherry picked from commit 9b1897b)

Author: rorth

clang/lib/Driver/ToolChains/Gnu.cpp

@@ -631,6 +631,16 @@ void tools::gnutools::Linker::ConstructJob(Compilation &C, const JobAction &JA,
 
       AddRunTimeLibs(ToolChain, D, CmdArgs, Args);
 
+      // LLVM support for atomics on 32-bit SPARC V8+ is incomplete, so
+      // forcibly link with libatomic as a workaround.
+      // TODO: Issue #41880 and D118021.
+      if (getToolChain().getTriple().getArch() == llvm::Triple::sparc) {
+        CmdArgs.push_back("--push-state");
+        CmdArgs.push_back("--as-needed");
+        CmdArgs.push_back("-latomic");
+        CmdArgs.push_back("--pop-state");
+      }
+
       if (WantPthread && !isAndroid)
         CmdArgs.push_back("-lpthread");
 

clang/test/Driver/linux-ld.c

@@ -1007,6 +1007,7 @@
 // CHECK-SPARCV8: "{{.*}}ld{{(.exe)?}}"
 // CHECK-SPARCV8: "-m" "elf32_sparc"
 // CHECK-SPARCV8: "-dynamic-linker" "{{(/usr/sparc-unknown-linux-gnu)?}}/lib/ld-linux.so.2"
+// CHECK-SPARCV8: "--push-state" "--as-needed" "-latomic" "--pop-state"
 //
 // RUN: %clang -### %s -no-pie 2>&1 \
 // RUN:     --target=sparcel-unknown-linux-gnu \
@@ -1021,6 +1022,7 @@
 // CHECK-SPARCV9: "{{.*}}ld{{(.exe)?}}"
 // CHECK-SPARCV9: "-m" "elf64_sparc"
 // CHECK-SPARCV9: "-dynamic-linker" "{{(/usr/sparcv9-unknown-linux-gnu)?}}/lib{{(64)?}}/ld-linux.so.2"
+// CHECK-SPARCV9-NOT: "-latomic"
 
 // Test linker invocation on Android.
 // RUN: %clang -### %s -no-pie 2>&1 \