snippet/_Noreturn: work around Clang _Noreturn bug
This is a bigger-hammer workaround for the clang _Noreturn issue
fix for dfa.c on 2023-01-01. Unfortunately, it causes 270
-Wreturn-type and -Wsometimes-uninitialized warnings when building
bleeding-edge GNU Emacs from Git on Fedora 37 with plain
‘./configure && make’. So the workaround is enabled only if you
compile with -D_GL_WORK_AROUND_LLVM_BUG_59792.
* lib/_Noreturn.h (_Noreturn):
* m4/gnulib-common.m4 (gl_COMMON_BODY):
and if _GL_WORK_AROUND_LLVM_BUG_59792 is defined.