Revert "[gn build] (manually) port bcdd40f802a5"

This reverts commit 0bd9d9aa3c.
bcdd40f802 was reverted in 4f9cc1512d

llvm/utils/gn/secondary/llvm/lib/Target/targets.gni

@@ -49,7 +49,6 @@ llvm_build_ARM = false
 llvm_build_BPF = false
 llvm_build_Mips = false
 llvm_build_PowerPC = false
-llvm_build_SystemZ = false
 llvm_build_WebAssembly = false
 llvm_build_X86 = false
 foreach(target, llvm_targets_to_build) {
@@ -65,8 +64,6 @@ foreach(target, llvm_targets_to_build) {
     llvm_build_Mips = true
   } else if (target == "PowerPC") {
     llvm_build_PowerPC = true
-  } else if (target == "SystemZ") {
-    llvm_build_SystemZ = true
   } else if (target == "WebAssembly") {
     llvm_build_WebAssembly = true
   } else if (target == "X86") {

llvm/utils/gn/secondary/llvm/unittests/BUILD.gn

@@ -80,9 +80,6 @@ group("unittests") {
       "tools/llvm-exegesis/PowerPC:LLVMExegesisPowerPCTests",
     ]
   }
-  if (llvm_build_SystemZ) {
-    deps += [ "MC/SystemZ:SystemZAsmLexer" ]
-  }
   if (llvm_build_WebAssembly) {
     deps += [ "Target/WebAssembly:WebAssemblyTests" ]
   }

llvm/utils/gn/secondary/llvm/unittests/MC/SystemZ/BUILD.gn

@@ -1,10 +0,0 @@
-import("//llvm/utils/unittest/unittest.gni")
-
-unittest("SystemZAsmLexer") {
-  deps = [
-    "//llvm/lib/MC",
-    "//llvm/lib/Support",
-    "//llvm/lib/Target/SystemZ",
-  ]
-  sources = [ "SystemZAsmLexerTest.cpp" ]
-}