jimtcl: don't attempt to handle ccache internally

jimtcl: don't attempt to handle ccache internally

jimtcl tries to use 'ccache' (a non-buildroot host version) which may not
exist on the host system. If ccache is enabled in buildroot, the compiler
used by jimtcl is:
ccache <buildroot>/.../ccache <buildroot>/.../<tuple>-gcc

If ccache is not present on the host, this results in the build error:

ccache <buildroot>/.../ccache <buildroot>/.../<tuple>-gcc
-D_GNU_SOURCE -Wall  -I. -fpic -pipe -Os    -c -o jim-subcmd.o jim-subcmd.c
make[1]: ccache: Command not found

This patch passes 'CCACHE=none' to the 'configure' script, disabling the
internal handling of ccache, so that ccache can be transparently passed
through CC.

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>