[Patch] BaseTools: Fix building FatPkg failed issue

[BobCF <bob.c.feng@intel.com>]

Using property instead of vairable for DecPcds.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Bob Feng <bob.c.feng@intel.com>
CC: Liming Gao <liming.gao@intel.com>
---
 BaseTools/Source/Python/Workspace/DscBuildData.py | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/BaseTools/Source/Python/Workspace/DscBuildData.py b/BaseTools/Source/Python/Workspace/DscBuildData.py
index b60c0fdf3..dcc70e8ba 100644
--- a/BaseTools/Source/Python/Workspace/DscBuildData.py
+++ b/BaseTools/Source/Python/Workspace/DscBuildData.py
@@ -1010,11 +1010,11 @@ class DscBuildData(PlatformBuildClassObject):
             else:
                 EdkLogger.error('build', PARSER_ERROR,
                             "Pcd (%s.%s) defined in DSC is not declared in DEC files. Arch: ['%s']" % (str_pcd[0], str_pcd[1], self._Arch),
                             File=self.MetaFile,Line = StrPcdSet[str_pcd][0][5])
         # Add the Structure PCD that only defined in DEC, don't have override in DSC file
-        for Pcd in self._DecPcds:
+        for Pcd in self.DecPcds:
             if type (self._DecPcds[Pcd]) is StructurePcd:
                 if Pcd not in S_pcd_set:
                     str_pcd_obj_str = StructurePcd()
                     str_pcd_obj_str.copy(self._DecPcds[Pcd])
                     str_pcd_obj = Pcds.get(Pcd, None)
@@ -1987,11 +1987,25 @@ class DscBuildData(PlatformBuildClassObject):
     #
     def AddPcd(self, Name, Guid, Value):
         if (Name, Guid) not in self.Pcds:
             self.Pcds[Name, Guid] = PcdClassObject(Name, Guid, '', '', '', '', '', {}, False, None)
         self.Pcds[Name, Guid].DefaultValue = Value
-
+    @property
+    def DecPcds(self):
+        if self._DecPcds == None:
+            FdfInfList = []
+            if GlobalData.gFdfParser:
+                FdfInfList = GlobalData.gFdfParser.Profile.InfList
+            PkgSet = set()
+            for Inf in FdfInfList:
+                ModuleFile = PathClass(NormPath(Inf), GlobalData.gWorkspace, Arch=self._Arch)
+                if ModuleFile in self._Modules:
+                    continue
+                ModuleData = self._Bdb[ModuleFile, self._Arch, self._Target, self._Toolchain]
+                PkgSet.update(ModuleData.Packages)
+            self._DecPcds = GetDeclaredPcd(self, self._Bdb, self._Arch, self._Target, self._Toolchain,PkgSet)
+        return self._DecPcds
     _Macros = property(_GetMacros)
     Arch = property(_GetArch, _SetArch)
     Platform = property(_GetPlatformName)
     PlatformName = property(_GetPlatformName)
     Guid = property(_GetFileGuid)
-- 
2.14.3.windows.1