stdio: Remove the usage of $(fno-unit-at-a-time) for errlist.c

stdio: Remove the usage of $(fno-unit-at-a-time) for errlist.c

The errlist.c is built with -fno-toplevel-reorder to avoid compiler to
reorder the compat assembly directives due an assembler issue [1]
(fixed on 2.39).

This patch removes the compiler flags by split the compat symbol
generation in two phases.  First the _sys_errlist_internal internal
without any compat symbol directive is preprocessed to generate an
assembly source code.  This generate assembly is then used as input
on a platform agnostic errlist-data.S which then creates the compat
definitions.  This prevents compiler to move any compat directive
prior the _sys_errlist_internal definition itself.

Checked on a make check run-built-tests=no on all affected ABIs.

[1] https://sourceware.org/bugzilla/show_bug.cgi?id=29012