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>

package/ccache/Config.in

@@ -0,0 +1,9 @@
+config BR2_PACKAGE_CCACHE
+	bool "ccache"
+	help
+	  ccache is a compiler cache. It speeds up recompilation by
+	  caching previous compilations and detecting when the same
+	  compilation is being done again
+
+	  http://samba.ccache.org
+

package/ccache/ccache.mk

@@ -0,0 +1,33 @@
+#############################################################
+#
+# ccache
+#
+#############################################################
+
+CCACHE_VERSION = 3.1.3
+CCACHE_SITE    = http://samba.org/ftp/ccache
+CCACHE_SOURCE  = ccache-$(CCACHE_VERSION).tar.bz2
+
+# When ccache is being built for the host, ccache is not yet
+# available, so we have to use the special C compiler without the
+# cache.
+HOST_CCACHE_CONF_ENV = \
+	CC="$(HOSTCC_NOCCACHE)"
+
+# We directly hardcode the cache location into the binary, as it is
+# much easier to handle than passing an environment variable.
+define HOST_CCACHE_FIX_CCACHE_DIR
+	sed -i 's,getenv("CCACHE_DIR"),"$(CCACHE_CACHE_DIR)",' $(@D)/ccache.c
+endef
+
+HOST_CCACHE_POST_CONFIGURE_HOOKS += \
+	HOST_CCACHE_FIX_CCACHE_DIR
+
+$(eval $(call AUTOTARGETS,package,ccache))
+$(eval $(call AUTOTARGETS,package,ccache,host))
+
+ifeq ($(BR2_CCACHE),y)
+ccache-stats: host-ccache
+	$(Q)$(CCACHE) -s
+endif
+