The solution for me in Xcode 12.5 is to add TARGET_OS_IPHONE or TARGET_OS_IPHONE=1 to GCC_PREPROCESSOR_DEFINITIONS_NOT_USED_IN_PRECOMPS in build settings or in an .xcconfig file.
Details:
After updating to Xcode 12.5 beta, now carthage bootstrap will fail when trying to build iRate 1.12.2. I looked in the carthage build log, and the error responsible for the failure is:
error: 'TARGET_OS_IPHONE' is not defined, evaluates to 0 [-Werror,-Wundef-prefix=TARGET_OS_]
The problem for me is that iRate is no longer under development, and I'd rather not fork iRate it just to override some broken build setting.
However, there is a nifty workaround trick that I learned from the folks over at Carthage: you can override the build settings of any project using any .xcconfig file by setting an environment variable, XCODE_XCCONFIG_FILE=path/to/my.xcconfig before running xcodebuild. Any settings in that .xcconfig file will now override the settings of whatever project you're building with xcodebuild.
Furthermore you can do this dynamically by a script that you call instead of calling xcodebuild, e.g.:
#!/usr/bin/env bash
# Save this script as 'injectXcodeBuild.sh'
# Run it in place of xcodebuild (all arguments get forwarded through)
# The echo'd commands below will override any settings of the
# projects that get built by xcodebuild through this script.
set -euo pipefail
xcconfig=$(mktemp /tmp/static.xcconfig.XXXXXX)
trap 'rm -f "$xcconfig"' INT TERM HUP EXIT
echo 'GCC_PREPROCESSOR_DEFINITIONS_NOT_USED_IN_PRECOMPS=TARGET_OS_IPHONE=1' >> $xcconfig
export XCODE_XCCONFIG_FILE="$xcconfig"
xcodebuild "$@"
Alternatively instead of xcodebuild this script could call carthage if you're needing to override some Carthage dependency's build settings. It might also work for CocoaPods pod command (I'm not sure).
