configure: disallow ccache during compile tests

If the user is using ccache during the configuration step,
it may interfere with some of the configuration tests,
particularly the "Is ccache interfering with macro analysis" step,
which is a bit of a poetic problem.

1) Disallow ccache from reading from the cache during configure,
   but don't disable it entirely to allow us to see if it causes other
   problems.

2) Force off CCACHE_CPP2 during the ccache test to get a deterministic
   answer over whether or not we need to enable that feature later.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-Id: <1446055000-29150-1-git-send-email-jsnow@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/configure b/configure
index 7a1d08dc4a..9c726ebada 100755
--- a/configure
+++ b/configure
@@ -8,6 +8,9 @@
 CLICOLOR_FORCE= GREP_OPTIONS=
 unset CLICOLOR_FORCE GREP_OPTIONS
 
+# Don't allow CCACHE, if present, to use cached results of compile tests!
+export CCACHE_RECACHE=yes
+
 # Temporary directory used for files created while
 # configure runs. Since it is in the build directory
 # we can safely blow away any previous version of it
@@ -4412,6 +4415,7 @@ fi
 # check if ccache is interfering with
 # semantic analysis of macros
 
+unset CCACHE_CPP2
 ccache_cpp2=no
 cat > $TMPC << EOF
 static const int Z = 1;