base.bbclass: Check BuildStarted for HOSTTOOLS

base.bbclass: Check BuildStarted for HOSTTOOLS

There might be no bb.event.ConfigParsed event if bitbake server is running, so
check bb.event.BuildStarted too to make sure HOSTTOOLS_DIR exists.

Fixed:
$ export BB_SERVER_TIMEOUT=-1
$ bitbake quilt-native
$ rm -fr tmp
$ bitbake quilt-native
ERROR: Error running gcc  --version: /bin/sh: gcc: command not found

This error is caused by enable_uninative(), it runs twice (ConfigParsed and
BuildStarted), the error would happen when there is no ConfigParsed event
(no hosttools is created), but BuildStarted. This patch can fix the problem.

[YOCTO #13022]

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>