BaseTools:build break if the Path contains SingleFile.Ext

BaseTools:build break if the Path contains SingleFile.Ext

BZ:https://bugzilla.tianocore.org/show_bug.cgi?id=1325

if SingleFile.Path = "/foo/bar.Sap/yada/source.S" and
SingleFile.Ext = ".S". Then key would end up "/foo/bar"
instead of "/foo/bar.Sap/yada/source" as intended.

Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Zhiju.Fan <zhijux.fan@intel.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>