[Driver] Allow XRay for more architectures on ELF systems

Codegen OS-agnostic for ELF and the runtime is mostly OS-agnostic. It
seems unnecessary to make restriction.

While here, rewrite test/Driver/XRay/xray-instrument*.c to be more conventional:
specify --target= explicitly instead of relying on the configured default target
(which needs `REQUIRES:`).

I am not sure enumerating every supported architecture is useful, so we just test a few.

clang/lib/Driver/XRayArgs.cpp

@@ -31,7 +31,12 @@ XRayArgs::XRayArgs(const ToolChain &TC, const ArgList &Args) {
                     options::OPT_fno_xray_instrument, false))
     return;
   XRayInstrument = Args.getLastArg(options::OPT_fxray_instrument);
-  if (Triple.getOS() == llvm::Triple::Linux) {
+  if (Triple.isMacOSX()) {
+    if (Triple.getArch() != llvm::Triple::x86_64) {
+      D.Diag(diag::err_drv_unsupported_opt_for_target)
+          << XRayInstrument->getSpelling() << Triple.str();
+    }
+  } else if (Triple.isOSBinFormatELF()) {
     switch (Triple.getArch()) {
     case llvm::Triple::x86_64:
     case llvm::Triple::arm:
@@ -47,21 +52,6 @@ XRayArgs::XRayArgs(const ToolChain &TC, const ArgList &Args) {
       D.Diag(diag::err_drv_unsupported_opt_for_target)
           << XRayInstrument->getSpelling() << Triple.str();
     }
-  } else if (Triple.isOSFreeBSD() || Triple.isOSOpenBSD() ||
-             Triple.isOSNetBSD() || Triple.isMacOSX()) {
-    if (Triple.getArch() != llvm::Triple::x86_64) {
-      D.Diag(diag::err_drv_unsupported_opt_for_target)
-          << XRayInstrument->getSpelling() << Triple.str();
-    }
-  } else if (Triple.getOS() == llvm::Triple::Fuchsia) {
-    switch (Triple.getArch()) {
-    case llvm::Triple::x86_64:
-    case llvm::Triple::aarch64:
-      break;
-    default:
-      D.Diag(diag::err_drv_unsupported_opt_for_target)
-          << XRayInstrument->getSpelling() << Triple.str();
-    }
   } else {
     D.Diag(diag::err_drv_unsupported_opt_for_target)
         << XRayInstrument->getSpelling() << Triple.str();

clang/test/Driver/XRay/xray-instrument.c

@@ -0,0 +1,8 @@
+// RUN: %clang -### --target=aarch64-pc-freebsd -fxray-instrument -c %s -o /dev/null 2>&1 | FileCheck %s
+// RUN: %clang -### --target=x86_64-apple-darwin -fxray-instrument -c %s -o /dev/null 2>&1 | FileCheck %s
+// RUN: %clang -### --target=x86_64-pc-windows -fxray-instrument -c %s -o /dev/null 2>&1 | FileCheck %s --check-prefix=ERR
+
+// CHECK: "-cc1" {{.*}}"-fxray-instrument"
+// ERR:   error: unsupported option '-fxray-instrument' for target
+
+typedef int a;