Revert 'Remove --gc-sections for all targets for now (#5707)' (#5735)

It should work with lld now that the lld flag '-z nostart-stop-gc' was added with
swiftlang/swift#60544 and swiftlang/swift-driver#1153.

Author: finagolfin

Sources/Build/BuildPlan.swift

@@ -1334,12 +1334,17 @@ public final class ProductBuildDescription {
                 return ["-Xlinker", "-dead_strip"]
             } else if buildParameters.triple.isWindows() {
                 return ["-Xlinker", "/OPT:REF"]
-            } else {
-                // FIXME: wasm-ld / ld.lld strips data segments referenced through __start/__stop symbols
+            } else if buildParameters.triple.arch == .wasm32 {
+                // FIXME: wasm-ld strips data segments referenced through __start/__stop symbols
                 // during GC, and it removes Swift metadata sections like swift5_protocols
                 // We should add support of SHF_GNU_RETAIN-like flag for __attribute__((retain))
                 // to LLVM and wasm-ld
+                // This workaround is required for not only WASI but also all WebAssembly archs
+                // using wasm-ld (e.g. wasm32-unknown-unknown). So this branch is conditioned by
+                // arch == .wasm32
                 return []
+            } else {
+                return ["-Xlinker", "--gc-sections"]
             }
         }
     }

Tests/BuildTests/BuildPlanTests.swift

@@ -446,6 +446,7 @@ final class BuildPlanTests: XCTestCase {
             "-o", buildPath.appending(components: "exe").pathString,
             "-module-name", "exe",
             "-emit-executable",
+            "-Xlinker", "--gc-sections",
             "-Xlinker", "-rpath=$ORIGIN",
             "@\(buildPath.appending(components: "exe.product", "Objects.LinkFileList"))",
             "-target", defaultTargetTriple,