wasm: add support for wasm32-unknown-wasi

This adds the initial conditional compilation support for the WASM32
"architecture" assuming that WASI is used as the "OS".  Support for
baremetal targets in Swift needs more work still, but this gives enough
infrastructure to start playing with WASM.

lib/Basic/LangOptions.cpp

@@ -39,6 +39,7 @@ static const StringRef SupportedConditionalCompilationOSs[] = {
   "PS4",
   "Cygwin",
   "Haiku",
+  "WASI",
 };
 
 static const StringRef SupportedConditionalCompilationArches[] = {
@@ -48,7 +49,8 @@ static const StringRef SupportedConditionalCompilationArches[] = {
   "x86_64",
   "powerpc64",
   "powerpc64le",
-  "s390x"
+  "s390x",
+  "wasm32",
 };
 
 static const StringRef SupportedConditionalCompilationEndianness[] = {
@@ -246,6 +248,9 @@ std::pair<bool, bool> LangOptions::setTarget(llvm::Triple triple) {
   case llvm::Triple::Haiku:
     addPlatformConditionValue(PlatformConditionKind::OS, "Haiku");
     break;
+  case llvm::Triple::WASI:
+    addPlatformConditionValue(PlatformConditionKind::OS, "WASI");
+    break;
   default:
     UnsupportedOS = true;
     break;
@@ -277,6 +282,9 @@ std::pair<bool, bool> LangOptions::setTarget(llvm::Triple triple) {
   case llvm::Triple::ArchType::systemz:
     addPlatformConditionValue(PlatformConditionKind::Arch, "s390x");
     break;
+  case llvm::Triple::ArchType::wasm32:
+    addPlatformConditionValue(PlatformConditionKind::Arch, "wasm32");
+    break;
   default:
     UnsupportedArch = true;
   }
@@ -291,6 +299,7 @@ std::pair<bool, bool> LangOptions::setTarget(llvm::Triple triple) {
   case llvm::Triple::ArchType::thumb:
   case llvm::Triple::ArchType::aarch64:
   case llvm::Triple::ArchType::ppc64le:
+  case llvm::Triple::ArchType::wasm32:
   case llvm::Triple::ArchType::x86:
   case llvm::Triple::ArchType::x86_64:
     addPlatformConditionValue(PlatformConditionKind::Endianness, "little");

test/Parse/ConditionalCompilation/wasm32Target.swift

@@ -0,0 +1,8 @@
+// RUN: %swift -typecheck %s -verify -target wasm32-unknown-wasi -disable-objc-interop -parse-stdlib
+// RUN: %swift-ide-test -test-input-complete -source-filename %s -target wasm32-unknown-wasi
+
+#if arch(wasm32) && os(WASI) && _runtime(_Native) && _endian(little)
+class C {}
+var x = C()
+#endif
+var y = x