[gn build] Port 6512a8d

Author: aeubanks

llvm/utils/gn/secondary/llvm/lib/Target/SystemZ/MCTargetDesc/BUILD.gn

@@ -52,8 +52,10 @@ static_library("MCTargetDesc") {
   include_dirs = [ ".." ]
   sources = [
     "SystemZELFObjectWriter.cpp",
+    "SystemZGNUInstPrinter.cpp",
     "SystemZGOFFObjectWriter.cpp",
-    "SystemZInstPrinter.cpp",
+    "SystemZHLASMInstPrinter.cpp",
+    "SystemZInstPrinterCommon.cpp",
     "SystemZMCAsmBackend.cpp",
     "SystemZMCAsmInfo.cpp",
     "SystemZMCCodeEmitter.cpp",