Ox: Attribute Grammar Compiling System libnew

- document significant change in the Libnew 1.2.1 release

- update Autoconf generated file due to change [r 193]

- bump the Libnew subminor version to 1.2.1

- update Automake generated file due to change [r 190]

- update Autoconf generated file due to change [r 190]

- special case handling for macOS Homebrew GNU C/C++ compiler versions 12-14: add flag '-mmacosx-version-min=<macOS major version>.0' to 'AM_CFLAGS/AM_CXXFLAGS'
- [regression testing]: the macOS Command Line Tools for Xcode 26.3 clang 'integrated assembler' warns about overriding deployment version from '16.0' to '26.0' invoked from these compilers
- special case handling for macOS Homebrew LLVM C/C++ compiler versions 16-20: add flag '-mmacosx-version-min=<macOS major version>.0' to 'AM_CFLAGS/AM_CXXFLAGS'
- [regression testing]: avoid warnings from the macOS Command Line Tools for Xcode 26.3 clang when linking with libraries built for macOS version 26.0
- drop special case handling for Homebrew C/C++ compiler version 5

- update Autoconf generated file due to change [r 188]

- remove macOS-specific parts of scripts related to use of the '-single_module' and '-multi_module' linker flags
- [regression testing]: macOS Command Line Tools for Xcode 26.3 linker warns that '-single-module' is obsolete; '-multi_module' is also obsolete

- update to Automake 1.18.1 versions

- update Autoconf generated file due to change [r 185]