BaseTools/Build: Consider only build-specified architectures

When building for any specific architecture, the build script today
is loading DSC sections for other architectures not in the build.
The build process should disregard DSC sections that are not
relevant to the build.

This fixes scenario whereby a build occurs in a source tree that was
been cleaned of non-essential directories.  For instance, X64 builds
do not require the ArmPkg directory to build a firmware image.  This
condition (build break when ArmPkg is absent) occurs when included
DSCs have sections for multiple architectures.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Thomas Palmer <thomas.palmer@hpe.com>
Reviewed-by: Yonghong Zhu <yonghong.zhu@intel.com>

BaseTools/Source/Python/Workspace/WorkspaceDatabase.py

@@ -2,6 +2,7 @@
 # This file is used to create a database used by build tool
 #
 # Copyright (c) 2008 - 2016, Intel Corporation. All rights reserved.<BR>
+# (C) Copyright 2016 Hewlett Packard Enterprise Development LP<BR>
 # This program and the accompanying materials
 # are licensed and made available under the terms and conditions of the BSD License
 # which accompanies this distribution.  The full text of the license may be found at
@@ -543,6 +544,13 @@ class DscBuildData(PlatformBuildClassObject):
         Macros["EDK_SOURCE"] = GlobalData.gEcpSource
         for Record in RecordList:
             DuplicatedFile = False
+
+            # process only records COMMON and self.Arch
+            SectionArch = Record[3].upper()
+            if SectionArch != 'COMMON':
+                if SectionArch != self.Arch:
+                    continue
+
             ModuleFile = PathClass(NormPath(Record[0], Macros), GlobalData.gWorkspace, Arch=self._Arch)
             ModuleId = Record[5]
             LineNo = Record[6]