ccache: rework ccache management

 * ccache is now a normal package (both for the host and the target).

 * ccache option is now part of the "Build options" menu. It will
   automatically build ccache for the host before building anything,
   and will use it to cache builds for both host compilations and
   target compilations.

 * bump ccache to 3.1.3

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
diff --git a/package/Config.in b/package/Config.in
index 08ffda6..b026828 100644
--- a/package/Config.in
+++ b/package/Config.in
@@ -35,7 +35,7 @@
 source "package/automake/Config.in"
 source "package/bison/Config.in"
 source "package/bsdiff/Config.in"
-source "toolchain/ccache/Config.in.2"
+source "package/ccache/Config.in"
 if BR2_PACKAGE_BUSYBOX_SHOW_OTHERS
 source "package/coreutils/Config.in"
 endif