Build failures on kernel version changes

[Julio Merino <jmmv%julipedia.org@localhost>]

Hello,

I always run "update builds" of the tree (in a cron job, for that 
matter) and, whenever the kernel version changes, the build breaks as 
shown here:

Configuring in ./libiberty
configure: loading cache ./config.cache
configure: error: `build_alias' has changed since the previous run:
configure:   former value:  `x86_64-unknown-netbsd5.99.55'
configure:   current value: `x86_64-unknown-netbsd5.99.58'
configure: error: `host_alias' has changed since the previous run:
configure:   former value:  `x86_64-unknown-netbsd5.99.55'
configure:   current value: `x86_64-unknown-netbsd5.99.58'
configure: error: in `/home/builder/obj/usr/src/tools/gcc/build/intl':
configure: error: changes in the environment can compromise the build
configure: error: run `make distclean' and/or `rm ./config.cache' and 
start over
configure: loading cache ./config.cache
nbgmake: *** [configure-intl] Error 1
nbgmake: *** Waiting for unfinished jobs....
configure: error: `build_alias' has changed since the previous run:
configure:   former value:  `x86_64-unknown-netbsd5.99.55'
configure:   current value: `x86_64-unknown-netbsd5.99.58'
configure: error: `host_alias' has changed since the previous run:
configure:   former value:  `x86_64-unknown-netbsd5.99.55'
configure:   current value: `x86_64-unknown-netbsd5.99.58'
configure: error: in `/home/builder/obj/usr/src/tools/gcc/build/libiberty':
configure: error: changes in the environment can compromise the build
configure: error: run `make distclean' and/or `rm ./config.cache' and 
start over
nbgmake: *** [configure-libiberty] Error 1

I understand why this happens, but after suffering from this issue for a 
long time, I was wondering...

Could we do something to automatically "workaround" this issue by, e.g. 
rebuilding all components that are affected by a kernel version change?

Or the only solution is to do a clean build in these cases?  If the 
answer is yes, then should build.sh just fallback to a clean build when 
it detects this condition to avoid the user-facing error?

Thanks.