cmake-native: prevent host libidn2 contamination

cmake-native: prevent host libidn2 contamination

The bundled cmcurl in CMake 4.3.x unconditionally enables USE_LIBIDN2
and calls find_package(Libidn2). On hosts with libidn2-devel installed
(common on RHEL/EL8), this detects the host library during configure
but the compile fails because the compiler is correctly restricted to
the native sysroot:

  fatal error: idn2.h: No such file or directory

This was introduced in the upgrade from CMake 3.28.x to 4.3.x, where
the bundled cmcurl added find_package(Libidn2) for IDN support.

cmake-native does not need IDN support in its internal curl usage.
Use CMAKE_DISABLE_FIND_PACKAGE_Libidn2 to prevent the host package
from being found without patching the source.

Signed-off-by: Jaipaul Cheernam <jaipaul.cheernam@est.tech>
Reviewed-by: Anders Heimer <anders.heimer@est.tech>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>