Add support for macOS Catalyst

[jnavarrom]

Allow to build cryptopp for macOS Catalyst, macOS Catalyst requires a specific target architecture.

Examples building for x86_64 and arm64 outputs

Using positional arg, MACOS_CPU=x86_64
Using positional arg, MACOS_CATALYST=1
Configuring for MacOSX (x86_64)
XCODE_TOOLCHAIN: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/
MACOS_SDK: MacOSX
MACOS_CPU: x86_64
MACOS_CFLAGS: -arch x86_64  -fno-common
MACOS_CXXFLAGS: -arch x86_64 -target x86_64-apple-ios15.0-macabi   -fno-common
MACOS_SYSROOT: /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.0.sdk
MACOS_CATALYST: 1

*******************************************************************************
It looks the the environment is set correctly. Your next step is build
the library with 'make -f GNUmakefile-cross'.
*******************************************************************************

Using testing flags: -DNDEBUG -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.0.sdk -g2 -O3 -fPIC -arch x86_64 -target x86_64-apple-ios15.0-macabi -fno-common
...

Using positional arg, MACOS_CPU=arm64
Using positional arg, MACOS_CATALYST=1
Configuring for MacOSX (arm64)
XCODE_TOOLCHAIN: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/
MACOS_SDK: MacOSX
MACOS_CPU: arm64
MACOS_CFLAGS: -arch arm64  -fno-common
MACOS_CXXFLAGS: -arch arm64 -target arm64-apple-ios15.0-macabi   -fno-common
MACOS_SYSROOT: /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.0.sdk
MACOS_CATALYST: 1

*******************************************************************************
It looks the the environment is set correctly. Your next step is build
the library with 'make -f GNUmakefile-cross'.
*******************************************************************************

Using testing flags: -DNDEBUG -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.0.sdk -g2 -O3 -fPIC -arch arm64 -target arm64-apple-ios15.0-macabi -fno-common
...