Mark start/stop sections as SHF_GNU_RETAIN

Fixes swiftlang/swift-package-manager#5698

Author: keith

lib/Driver/UnixToolChains.cpp

@@ -214,17 +214,6 @@ toolchains::GenericUnix::constructInvocation(const DynamicLinkJobAction &job,
 #else
     Arguments.push_back(context.Args.MakeArgString("-fuse-ld=" + Linker));
 #endif
-    // Starting with lld 13, Swift stopped working with the lld --gc-sections
-    // implementation for ELF, unless -z nostart-stop-gc is also passed to lld:
-    //
-    // https://reviews.llvm.org/D96914
-    if (Linker == "lld" || (Linker.length() > 5 &&
-                            Linker.substr(Linker.length() - 6) == "ld.lld")) {
-      Arguments.push_back("-Xlinker");
-      Arguments.push_back("-z");
-      Arguments.push_back("-Xlinker");
-      Arguments.push_back("nostart-stop-gc");
-    }
   }
 
   // Configure the toolchain.

stdlib/public/runtime/SwiftRT-ELF-WASM.cpp

@@ -36,7 +36,7 @@ static const void *__backtraceRef __attribute__((used))
 // by the linker.  Otherwise, we may end up with undefined symbol references as
 // the linker table section was never constructed.
 #if defined(__ELF__)
-# define DECLARE_EMPTY_METADATA_SECTION(name) __asm__("\t.section " #name ",\"a\"\n");
+# define DECLARE_EMPTY_METADATA_SECTION(name) __asm__("\t.section " #name ",\"aR\"\n");
 #elif defined(__wasm__)
 # define DECLARE_EMPTY_METADATA_SECTION(name) __asm__("\t.section " #name ",\"\",@\n");
 #endif

test/Driver/link-time-opt.swift

@@ -14,7 +14,6 @@
 // CHECK-SIMPLE-THIN-linux-gnu: clang
 // CHECK-SIMPLE-THIN-linux-gnu-DAG: -flto=thin
 // CHECK-SIMPLE-THIN-linux-gnu-DAG: -fuse-ld=lld
-// CHECK-SIMPLE-THIN-linux-gnu-DAG: -Xlinker -z -Xlinker nostart-stop-gc
 // CHECK-SIMPLE-THIN-linux-gnu-DAG: [[BITCODEFILE]]
 // CHECK-SIMPLE-THIN-linux-gnu-NOT: swift-autolink-extract
 
@@ -36,7 +35,6 @@
 // CHECK-SIMPLE-FULL-linux-gnu: clang
 // CHECK-SIMPLE-FULL-linux-gnu-DAG: -flto=full
 // CHECK-SIMPLE-FULL-linux-gnu-DAG: -fuse-ld=lld
-// CHECK-SIMPLE-FULL-linux-gnu-DAG: -Xlinker -z -Xlinker nostart-stop-gc
 // CHECK-SIMPLE-FULL-linux-gnu-DAG: [[BITCODEFILE]]
 // CHECK-SIMPLE-FULL-linux-gnu-NOT: swift-autolink-extract