BaseTools: introduce !error statement

BaseTools: introduce !error statement

The DSC and FDF file can use `!error` statement. The argument of this
statement is an error message, it causes build tool to stop at the
location where the statement is encountered and error message following
the `!error` statement is output as a message.

Fixes: https://bugzilla.tianocore.org/show_bug.cgi?id=701
Cc: Liming Gao <liming.gao@intel.com>
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Yunhua Feng <yunhuax.feng@intel.com>
Reviewed-by: Yonghong Zhu <yonghong.zhu@intel.com>