Stop using --gc-sections for Wasm target to protect metadata sections (#5638)

Now 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. For now, just disable section GC for Wasm target.

Context:
llvm/llvm-project#55839
https://reviews.llvm.org/D126950#3558050

Author: kateinoigakukun

Sources/Build/BuildPlan.swift

@@ -1294,6 +1294,15 @@ public final class ProductBuildDescription {
                 return ["-Xlinker", "-dead_strip"]
             } else if buildParameters.triple.isWindows() {
                 return ["-Xlinker", "/OPT:REF"]
+            } 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"]
             }