Basic: use switch instead of cascading if's

Rather than have a series of cascading if conditionals, use a switch.  Although
Darwin and android are special, they can be handled just as cleanly in the
switch version.  NFC.

Author: compnerd

lib/Basic/Platform.cpp

@@ -85,22 +85,43 @@ static StringRef getPlatformNameForDarwin(const DarwinPlatformKind platform) {
 }
 
 StringRef swift::getPlatformNameForTriple(const llvm::Triple &triple) {
-  if (triple.isOSDarwin())
+  switch (triple.getOS()) {
+  case llvm::Triple::UnknownOS:
+    llvm_unreachable("unknown OS");
+  case llvm::Triple::CloudABI:
+  case llvm::Triple::DragonFly:
+  case llvm::Triple::KFreeBSD:
+  case llvm::Triple::Lv2:
+  case llvm::Triple::NetBSD:
+  case llvm::Triple::OpenBSD:
+  case llvm::Triple::Solaris:
+  case llvm::Triple::Haiku:
+  case llvm::Triple::Minix:
+  case llvm::Triple::RTEMS:
+  case llvm::Triple::NaCl:
+  case llvm::Triple::CNK:
+  case llvm::Triple::Bitrig:
+  case llvm::Triple::AIX:
+  case llvm::Triple::CUDA:
+  case llvm::Triple::NVCL:
+  case llvm::Triple::AMDHSA:
+  case llvm::Triple::PS4:
+  case llvm::Triple::ELFIAMCU:
+    return "";
+  case llvm::Triple::Darwin:
+  case llvm::Triple::MacOSX:
+  case llvm::Triple::IOS:
+  case llvm::Triple::TvOS:
+  case llvm::Triple::WatchOS:
     return getPlatformNameForDarwin(getDarwinPlatformKind(triple));
-
-  if (triple.isAndroid())
-    return "android";
-
-  if (triple.isOSLinux())
-    return "linux";
-
-  if (triple.isOSFreeBSD())
+  case llvm::Triple::Linux:
+    return triple.isAndroid() ? "android" : "linux";
+  case llvm::Triple::FreeBSD:
     return "freebsd";
-
-  if (triple.isOSWindows())
-    return  "windows";
-
-  return "";
+  case llvm::Triple::Win32:
+    return "windows";
+  }
+  llvm_unreachable("unsupported OS");
 }
 
 StringRef swift::getMajorArchitectureName(const llvm::Triple &Triple) {