ccache: don't export CCACHE_DISABLE globally

CCACHE_DISABLE was added to bitbake.conf in oe-core dd2bab (June 2012) because
autogen-native exports HOME=/dev/null during the build, which is then used by a
host ccache to construct the path to it's cache (/dev/null/.ccache) and this
fails.

However we now always export CCACHE_DIR to solve the same problem in a more
efficient way so CCACHE_DISABLE can be deleted.

(From OE-Core rev: ef33a3138384667f819688141086102e6e83ec44)

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/ccache.bbclass

@@ -1,6 +1,5 @@
 CCACHE = "${@bb.utils.which(d.getVar('PATH'), 'ccache') and 'ccache '}"
 export CCACHE_DIR ?= "${TMPDIR}/ccache/${MULTIMACH_TARGET_SYS}/${PN}"
-CCACHE_DISABLE[unexport] = "1"
 
 # We need to stop ccache considering the current directory or the
 # debug-prefix-map target directory to be significant when calculating

meta/conf/bitbake.conf

@@ -480,9 +480,6 @@ HOSTTOOLS_NONFATAL += "aws ccache gcc-ar gpg ld.bfd ld.gold nc sftp socat sudo"
 HOSTTOOLS_NONFATAL += "join nl size yes zcat"
 
 CCACHE ??= ""
-# Disable ccache explicitly if CCACHE is null since gcc may be a symlink
-# of ccache some distributions (e.g., Fedora 17).
-export CCACHE_DISABLE ??= "${@[0,1][d.getVar('CCACHE') == '']}"
 # ccache < 3.1.10 will create CCACHE_DIR on startup even if disabled, and
 # autogen sets HOME=/dev/null so in certain situations builds can fail.
 # Explicitly export CCACHE_DIR until we can assume ccache >3.1.10 on the host.
@@ -845,7 +842,7 @@ BB_HASHBASE_WHITELIST ?= "TMPDIR FILE PATH PWD BB_TASKHASH BBPATH BBSERVER DL_DI
     SSTATE_DIR THISDIR FILESEXTRAPATHS FILE_DIRNAME HOME LOGNAME SHELL TERM \
     USER FILESPATH STAGING_DIR_HOST STAGING_DIR_TARGET COREBASE PRSERV_HOST \
     PRSERV_DUMPDIR PRSERV_DUMPFILE PRSERV_LOCKDOWN PARALLEL_MAKE \
-    CCACHE_DIR EXTERNAL_TOOLCHAIN CCACHE CCACHE_DISABLE LICENSE_PATH SDKPKGSUFFIX \
+    CCACHE_DIR EXTERNAL_TOOLCHAIN CCACHE LICENSE_PATH SDKPKGSUFFIX \
     WARN_QA ERROR_QA WORKDIR STAMPCLEAN PKGDATA_DIR BUILD_ARCH SSTATE_PKGARCH \
     BB_WORKERCONTEXT BB_LIMITEDDEPS extend_recipe_sysroot DEPLOY_DIR"
 BB_HASHCONFIG_WHITELIST ?= "${BB_HASHBASE_WHITELIST} DATE TIME SSH_AGENT_PID \