CI: Removes CMakeCache.txt between builds.

If the cache file is not removed, CMake will not reset configurations
back to their default values. In order to make the tests independent, it
is simplest to purge the cache. Unfortunatly, this will slow down the
tests a little and repeat some checks.

build-aux/ci_build.sh

@@ -218,6 +218,8 @@ then
 		# CMake disables the shared library by default.
 		add_extra_option "$SHARED" "-DBUILD_SHARED_LIBS=ON" ""
 
+		# Remove old cache file to clear previous settings.
+		rm -f "CMakeCache.txt"
 		cmake "$SRC_DIR/CMakeLists.txt" -B "$DEST_DIR" $EXTRA_OPTIONS -DADDITIONAL_CHECK_TYPES="$CHECK_TYPE"
 		make
 	;;