meson: fix support for iOS

The branch was compiled with:

meson setup build-iphoneos-arm64-meson --cross-file=iphone2.crossfile  --cross-file=/Users/unidan/Workspace/vlc/build-macosx/contrib/arm64-iphoneos/share/meson/cross/contrib.ini -Dlua=disabled -Drist=disabled --reconfigure

With:

╰─$ cat iphone2.crossfile
[binaries]
c = ['/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang', '-mios-version-min=9.0', '-arch', 'arm64', '-isysroot', '/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS16.2.sdk']
cpp = ['/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++', '-mios-version-min=9.0', '-arch', 'arm64', '-isysroot', '/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS16.2.sdk']
objc = ['/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang', '-mios-version-min=9.0', '-arch', 'arm64', '-isysroot', '/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS16.2.sdk']
objcpp = ['/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++', '-mios-version-min=9.0', '-arch', 'arm64', '-isysroot', '/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS16.2.sdk']
ar = '/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ar'
strip = '/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/strip'
pkgconfig = 'pkg-config'
c_args = ['-Werror=partial-availability']
cpp_args = ['-Werror=partial-availability']
objc_args = ['-Werror=partial-availability']
c_link_args = ['-arch', 'arm64', '-mios-version-min=9.0']


[properties]
#needs_exe_wrapper = true
vendor = 'apple'
target_dir = 'apple-iphoneos9.0-arm64-little'

[host_machine]
system = 'darwin'
cpu_family = 'aarch64'
endian = 'little'
cpu = 'aarch64'

[build_machine]
c = 'clang'

[cmake]
CMAKE_C_COMPILER = '/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang'
CMAKE_CXX_COMPILER = '/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++'

And the contrib machine file being generated by make .meson-machinefile.