Makefile: don't run configure for make clean

Normally we auto-run the configure part, if config-host.mak
doesn't exist. But we don't need to do that for make clean.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/Makefile b/Makefile
index 57f3f82..3de9735 100644
--- a/Makefile
+++ b/Makefile
@@ -6,8 +6,10 @@
 	@sed -n "/.*Configured with/s/[^:]*: //p" $@ | sh
 else
 config-host.mak:
+ifneq ($(MAKECMDGOALS),clean)
 	@echo "Running configure for you..."
 	@./configure
+endif
 all:
 include config-host.mak
 endif