misc/ios: rework exec wrapper to only support simulator

This updates the tools used to execute Go binaries on the Apple iOS
Simulator to (a) work with newer arm64 macOS, (b) remove support
for running binaries on physical devices, and (c) remove the reliance on
LLDB and third-party Python packages. This makes the wrapper somewhat
simpler, and easier to understand and maintain. Additionally
clangwrap.sh is updated to reflect dropping support for targeting
physical devices.

This smoothes out the path for #66360.

Change-Id: I769127e65f5e8c6c727841168890fd8557fb0e1d
Reviewed-on: https://go-review.googlesource.com/c/go/+/573175
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

misc/ios/clangwrap.sh

@@ -1,19 +1,22 @@
 #!/bin/sh
-# This uses the latest available iOS SDK, which is recommended.
-# To select a specific SDK, run 'xcodebuild -showsdks'
-# to see the available SDKs and replace iphoneos with one of them.
+
+# This script configures clang to target the iOS simulator. If you'd like to
+# build for real iOS devices, change SDK to "iphoneos" and PLATFORM to "ios".
+# This uses the latest available iOS SDK, which is recommended. To select a
+# specific SDK, run 'xcodebuild -showsdks' to see the available SDKs and replace
+# iphonesimulator with one of them.
+
+SDK=iphonesimulator
+PLATFORM=ios-simulator
+
 if [ "$GOARCH" == "arm64" ]; then
-	SDK=iphoneos
-	PLATFORM=ios
 	CLANGARCH="arm64"
 else
-	SDK=iphonesimulator
-	PLATFORM=ios-simulator
 	CLANGARCH="x86_64"
 fi
 
 SDK_PATH=`xcrun --sdk $SDK --show-sdk-path`
-export IPHONEOS_DEPLOYMENT_TARGET=5.1
+
 # cmd/cgo doesn't support llvm-gcc-4.2, so we have to use clang.
 CLANG=`xcrun --sdk $SDK --find clang`