[test][wasm][arm64] Fix JumpTablePatchingStress

This test attempted to call mprotect to switch memory permissions,
which returns an error on MacOS on arm64. The workaround is simple:
don't call mprotect, rely on MacOS-specific permission switching.

See also https://chromium-review.googlesource.com/c/v8/v8/+/2679688
for a related fix in non-test code.

Drive-by: fix host arch detection in gm.py when building on M1 Macs.

Bug: v8:11657
Change-Id: I9b59ee8f2279e28f7561ac071df27508211741f3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2831877Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74030}

test/cctest/wasm/test-jump-table-assembler.cc

@@ -156,8 +156,14 @@ void CompileJumpTableThunk(Address thunk, Address jump_target) {
   __ Ret();
 
   FlushInstructionCache(thunk, kThunkBufferSize);
+#if defined(V8_OS_MACOSX) && defined(V8_HOST_ARCH_ARM64)
+  // MacOS on arm64 refuses {mprotect} calls to toggle permissions of RWX
+  // memory. Simply do nothing here, and rely on
+  // {SwitchMemoryPermissionsToExecutable} in the JumpTableRunner.
+#else
   CHECK(SetPermissions(GetPlatformPageAllocator(), thunk, kThunkBufferSize,
                        v8::PageAllocator::kReadExecute));
+#endif
 }
 
 class JumpTableRunner : public v8::base::Thread {

tools/dev/gm.py

@@ -262,10 +262,10 @@ class Config(object):
       cpu = "arm"
     elif self.arch == "android_arm64":
       cpu = "arm64"
-    elif self.arch == "arm64" and _GetMachine() == "aarch64":
+    elif self.arch == "arm64" and _GetMachine() in ("aarch64", "arm64"):
       # arm64 build host:
       cpu = "arm64"
-    elif self.arch == "arm" and _GetMachine() == "aarch64":
+    elif self.arch == "arm" and _GetMachine() in ("aarch64", "arm64"):
       cpu = "arm"
     elif "64" in self.arch or self.arch == "s390x":
       # Native x64 or simulator build.
@@ -291,7 +291,8 @@ class Config(object):
 
   def GetSpecialCompiler(self):
     if _GetMachine() == "aarch64":
-      # We have no prebuilt Clang for arm64. Use the system Clang instead.
+      # We have no prebuilt Clang for arm64 on Linux, so use the system Clang
+      # instead.
       return ["clang_base_path = \"/usr\"", "clang_use_chrome_plugins = false"]
     return []