iOS: CMake 3.17 crash on missing per-architecture sysroots
after upgrade to cmake 3.17. any generator except xcode with `-DCMAKE_SYSTEM_NAME=iOS` will crash. ``` cmake .. -DCMAKE_SYSTEM_NAME=iOS "-DCMAKE_OSX_ARCHITECTURES=armv7;armv7s;arm64;i386;x86_64" -DCMAKE_OSX_DEPLOYMENT_TARGET=9.3 CMake Warning at cmake-3.17.0-Darwin-x86_64/CMake.app/Contents/share/cmake-3.17/Modules/Platform/Darwin-Initialize.cmake:204 (message): No SDK found for architecture 'armv7' Call Stack (most recent call first): cmake-3.17.0-Darwin-x86_64/CMake.app/Contents/share/cmake-3.17/Modules/Platform/Darwin-Initialize.cmake:213 (_apple_resolve_multi_arch_sysroots) cmake-3.17.0-Darwin-x86_64/CMake.app/Contents/share/cmake-3.17/Modules/Platform/iOS-Initialize.cmake:1 (include) cmake-3.17.0-Darwin-x86_64/CMake.app/Contents/share/cmake-3.17/Modules/CMakeSystemSpecificInitialize.cmake:21 (include) CMakeLists.txt:2 (project) CMake Warning at cmake-3.17.0-Darwin-x86_64/CMake.app/Contents/share/cmake-3.17/Modules/Platform/Darwin-Initialize.cmake:204 (message): No SDK found for architecture 'armv7s' Call Stack (most recent call first): cmake-3.17.0-Darwin-x86_64/CMake.app/Contents/share/cmake-3.17/Modules/Platform/Darwin-Initialize.cmake:213 (_apple_resolve_multi_arch_sysroots) cmake-3.17.0-Darwin-x86_64/CMake.app/Contents/share/cmake-3.17/Modules/Platform/iOS-Initialize.cmake:1 (include) cmake-3.17.0-Darwin-x86_64/CMake.app/Contents/share/cmake-3.17/Modules/CMakeSystemSpecificInitialize.cmake:21 (include) CMakeLists.txt:2 (project) CMake Warning at cmake-3.17.0-Darwin-x86_64/CMake.app/Contents/share/cmake-3.17/Modules/Platform/Darwin-Initialize.cmake:204 (message): No SDK found for architecture 'i386' Call Stack (most recent call first): cmake-3.17.0-Darwin-x86_64/CMake.app/Contents/share/cmake-3.17/Modules/Platform/Darwin-Initialize.cmake:213 (_apple_resolve_multi_arch_sysroots) cmake-3.17.0-Darwin-x86_64/CMake.app/Contents/share/cmake-3.17/Modules/Platform/iOS-Initialize.cmake:1 (include) cmake-3.17.0-Darwin-x86_64/CMake.app/Contents/share/cmake-3.17/Modules/CMakeSystemSpecificInitialize.cmake:21 (include) CMakeLists.txt:2 (project) -- The C compiler identification is AppleClang 11.0.3.11030032 -- The CXX compiler identification is AppleClang 11.0.3.11030032 -- Check for working C compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/cc cmake(65662,0x10ef1adc0) malloc: can't allocate region :*** mach_vm_map(size=8459008377403949056, flags: 60000100) failed (error code=3) cmake(65662,0x10ef1adc0) malloc: *** set a breakpoint in malloc_error_break to debug libc++abi.dylib: terminating with uncaught exception of type std::bad_alloc: std::bad_alloc [1] 65662 abort ../cmake-3.17.0-Darwin-x86_64/CMake.app/Contents/bin/cmake .. ```
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