Detect missing GNU_PROPERTY_X86_FEATURE_1_SHSTK in ELF files.

Shadow stack support was added to CFLAGS and CXXFLAGS with -fcf-protection as part of RFC 0003-buildflags.rst 1. glibc 2 / binutils 3 detect shadow stack support by checking for GNU_PROPERTY_X86_FEATURE_1_SHSTK in .note.gnu.property notes section of the generated ELF binary record. Kernel support for userspace shadow stacks was added in linux 6.6 4. There is currently no detection in namcap if GNU_PROPERTY_X86_FEATURE_1_SHSTK is present. Support may be missing for example due to the package having not been rebuilt since the build flags were updated or the project not using the flags or the project using assembler.