[linux-port] Define LLVMBuild.txt for DxcSupport. (#1292)

Also add missing dependencies for lib/HLSL.

These dependencies only manifest themselves in Debug mode.

lib/DxcSupport/LLVMBuild.txt

@@ -0,0 +1,21 @@
+;===- ./lib/DxcSupport/LLVMBuild.txt ---------------------------*- Conf -*--===;
+;
+;                     The LLVM Compiler Infrastructure
+;
+; This file is distributed under the University of Illinois Open Source
+; License. See LICENSE.TXT for details.
+;
+;===------------------------------------------------------------------------===;
+;
+; This is an LLVMBuild description file for the components in this subdirectory.
+;
+; For more information on the LLVMBuild system, please see:
+;
+;   http://llvm.org/docs/LLVMBuild.html
+;
+;===------------------------------------------------------------------------===;
+
+[component_0]
+type = Library
+name = DxcSupport
+parent = Libraries

lib/HLSL/LLVMBuild.txt

@@ -13,4 +13,4 @@
 type = Library
 name = HLSL
 parent = Libraries
-required_libraries = Core Support
+required_libraries = BitReader Core DxcSupport IPA Support

lib/LLVMBuild.txt

@@ -22,6 +22,7 @@ subdirectories =
  Bitcode
  CodeGen
  DebugInfo
+ DxcSupport
  ExecutionEngine
  Linker
  IR