Index: lib/Driver/ToolChain.cpp
===================================================================
--- lib/Driver/ToolChain.cpp
+++ lib/Driver/ToolChain.cpp
@@ -309,8 +309,12 @@
 
 std::string ToolChain::getCompilerRTPath() const {
   SmallString<128> Path(getDriver().ResourceDir);
-  StringRef OSLibName = Triple.isOSFreeBSD() ? "freebsd" : getOS();
-  llvm::sys::path::append(Path, "lib", OSLibName);
+  if (Triple.isOSUnknown()) {
+    llvm::sys::path::append(Path, "lib");
+  } else {
+    StringRef OSLibName = Triple.isOSFreeBSD() ? "freebsd" : getOS();
+    llvm::sys::path::append(Path, "lib", OSLibName);
+  }
   return Path.str();
 }
 
Index: lib/Driver/ToolChains/CommonArgs.cpp
===================================================================
--- lib/Driver/ToolChains/CommonArgs.cpp
+++ lib/Driver/ToolChains/CommonArgs.cpp
@@ -1027,15 +1027,7 @@
 
   switch (RLT) {
   case ToolChain::RLT_CompilerRT:
-    switch (TC.getTriple().getOS()) {
-    default:
-      llvm_unreachable("unsupported OS");
-    case llvm::Triple::Win32:
-    case llvm::Triple::Linux:
-    case llvm::Triple::Fuchsia:
-      CmdArgs.push_back(TC.getCompilerRTArgString(Args, "builtins"));
-      break;
-    }
+    CmdArgs.push_back(TC.getCompilerRTArgString(Args, "builtins"));
     break;
   case ToolChain::RLT_Libgcc:
     // Make sure libgcc is not used under MSVC environment by default
Index: lib/Driver/ToolChains/WebAssembly.cpp
===================================================================
--- lib/Driver/ToolChains/WebAssembly.cpp
+++ lib/Driver/ToolChains/WebAssembly.cpp
@@ -49,6 +49,9 @@
   Args.AddAllArgs(CmdArgs, options::OPT_L);
   ToolChain.AddFilePathLibArgs(Args, CmdArgs);
 
+  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles))
+    CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath("crt1.o")));
+
   AddLinkerInputs(ToolChain, Inputs, Args, CmdArgs, JA);
 
   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
@@ -61,7 +64,7 @@
     CmdArgs.push_back("-allow-undefined-file");
     CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath("wasm.syms")));
     CmdArgs.push_back("-lc");
-    CmdArgs.push_back("-lcompiler_rt");
+    AddRunTimeLibs(ToolChain, ToolChain.getDriver(), CmdArgs, Args);
   }
 
   CmdArgs.push_back("-o");
Index: test/Driver/wasm-toolchain.c
===================================================================
--- test/Driver/wasm-toolchain.c
+++ test/Driver/wasm-toolchain.c
@@ -27,10 +27,10 @@
 
 // RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-unknown --sysroot=/foo %s 2>&1 | FileCheck -check-prefix=LINK %s
 // LINK: clang{{.*}}" "-cc1" {{.*}} "-o" "[[temp:[^"]*]]"
-// LINK: lld{{.*}}" "-flavor" "wasm" "-L/foo/lib" "[[temp]]" "-allow-undefined-file" "wasm.syms" "-lc" "-lcompiler_rt" "-o" "a.out"
+// LINK: lld{{.*}}" "-flavor" "wasm" "-L/foo/lib" "crt1.o" "[[temp]]" "-allow-undefined-file" "wasm.syms" "-lc" "{{.*}}/libclang_rt.builtins-wasm32.a" "-o" "a.out"
 
 // A basic C link command-line with optimization.
 
 // RUN: %clang -### -O2 -no-canonical-prefixes -target wasm32-unknown-unknown --sysroot=/foo %s 2>&1 | FileCheck -check-prefix=LINK_OPT %s
 // LINK_OPT: clang{{.*}}" "-cc1" {{.*}} "-o" "[[temp:[^"]*]]"
-// LINK_OPT: lld{{.*}}" "-flavor" "wasm" "-L/foo/lib" "[[temp]]" "-allow-undefined-file" "wasm.syms" "-lc" "-lcompiler_rt" "-o" "a.out"
+// LINK_OPT: lld{{.*}}" "-flavor" "wasm" "-L/foo/lib" "crt1.o" "[[temp]]" "-allow-undefined-file" "wasm.syms" "-lc" "{{.*}}/libclang_rt.builtins-wasm32.a" "-o" "a.out"