clang-cross: Create <cross>-clang binary copy instead of symlink

clang-cross: Create <cross>-clang binary copy instead of symlink

With clang cleanup in [1] we ended up removing this logic, which
is still required.

This ensures that search path for subsequent tools e.g. linker
assembler are searched in the same dir where <cross>-clang is
installed. If its a symlink to ../clang then the reference
installation dir is ../ and all cross-tools are not there
so clang will fail to find assembler/linker from cross staging
area and use /usr/bin/ld or /usr/bin/as  which we do not want

[1] https://git.openembedded.org/openembedded-core/commit/meta/recipes-devtools/clang/clang-cross_git.bb?id=5d96ed55acf7b9a908241222097ad809355de7cf

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Cc: Ross Burton <ross.burton@arm.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>