gawk: use native gawk when building glibc and grub

gawk: use native gawk when building glibc and grub

Different versions of gawk can produce different output,
so depending on which version is installed on the build host,
reproducibility issues can occur:
https://bugzilla.yoctoproject.org/show_bug.cgi?id=16072

So far only glibc and grub have been identified to have
the issue; probably more fixes of similar nature will be
required going forward.

Adjust the gawk recipe to apply target-only tweaks
(particularly the removal of awk symlink to allow for alternatives)
to only target and nativesdk variants, so that native installs
both awk and gawk executables.

[YOCTO #16072]

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>