[lld][WebAssembly] Add support for LLD_REPRODUCE

This is feature of the ELF and COFF linker that we were missing until
now.

Differential Revision: https://reviews.llvm.org/D137377

lld/test/wasm/reproduce.s

@@ -0,0 +1,32 @@
+# REQUIRES: shell
+# RUN: rm -rf %t.dir
+# RUN: mkdir -p %t.dir
+# RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown -o %t.dir/foo.o %s
+# RUN: wasm-ld --reproduce=%t.dir/repro.tar -o %t.dir/out.wasm %t.dir/foo.o
+# RUN: env LLD_REPRODUCE=%t.dir/repro2.tar wasm-ld -o %t.dir/out.wasm %t.dir/foo.o
+
+# RUN: cd %t.dir
+# RUN: tar tf repro.tar | FileCheck --check-prefix=TAR %s
+# RUN: tar tf repro2.tar | FileCheck --check-prefix=TAR2 %s
+
+# TAR: repro/response.txt
+# TAR: repro/version.txt
+# TAR: repro/{{.*}}/foo.o
+
+# TAR2: repro2/response.txt
+# TAR2: repro2/version.txt
+# TAR2: repro2/{{.*}}/foo.o
+
+# RUN: tar xf repro.tar
+# RUN: FileCheck --check-prefix=RSP %s < repro/response.txt
+
+# RSP: -o {{.*}}out.wasm
+# RSP: {{.*}}/foo.o
+
+# RUN: FileCheck %s --check-prefix=VERSION < repro/version.txt
+# VERSION: LLD
+
+.globl  _start
+_start:
+  .functype _start () -> ()
+  end_function

lld/wasm/Driver.cpp

@@ -618,6 +618,12 @@ static void checkOptions(opt::InputArgList &args) {
   }
 }
 
+static const char *getReproduceOption(opt::InputArgList &args) {
+  if (auto *arg = args.getLastArg(OPT_reproduce))
+    return arg->getValue();
+  return getenv("LLD_REPRODUCE");
+}
+
 // Force Sym to be entered in the output. Used for -u or equivalent.
 static Symbol *handleUndefined(StringRef name) {
   Symbol *sym = symtab->find(name);
@@ -955,8 +961,7 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
   }
 
   // Handle --reproduce
-  if (auto *arg = args.getLastArg(OPT_reproduce)) {
-    StringRef path = arg->getValue();
+  if (const char *path = getReproduceOption(args)) {
     Expected<std::unique_ptr<TarWriter>> errOrWriter =
         TarWriter::create(path, path::stem(path));
     if (errOrWriter) {