gn build: Fix build when not building the native target.

[thakis]

LG, but please watch http://45.33.8.238/ after landing for 20 min or so.

llvm/utils/gn/secondary/llvm/include/llvm/Config/BUILD.gn

values = [
     "LLVM_DEFAULT_TARGET_TRIPLE=$llvm_target_triple",
     "LLVM_ENABLE_DUMP=",
     "LLVM_FORCE_ENABLE_STATS=",
     "LLVM_FORCE_USE_OLD_TOOLCHAIN=",
     "LLVM_HAS_ATOMICS=1",
     "LLVM_HAVE_TF_API=",
     "LLVM_HOST_TRIPLE=$llvm_current_triple",
     "LLVM_NATIVE_ARCH=$native_target",
-    "LLVM_NATIVE_ASMPARSER=1",
-    "LLVM_NATIVE_ASMPRINTER=1",
-    "LLVM_NATIVE_DISASSEMBLER=1",
-    "LLVM_NATIVE_TARGET=1",
-    "LLVM_NATIVE_TARGETINFO=1",
-    "LLVM_NATIVE_TARGETMC=1",
-    "LLVM_NATIVE_TARGETMCA=1",
     "LLVM_UNREACHABLE_OPTIMIZE=1",
     "LLVM_USE_INTEL_JITEVENTS=",
     "LLVM_USE_OPROFILE=",
     "LLVM_USE_PERF=",
     "LLVM_VERSION_MAJOR=$llvm_version_major",
     "LLVM_VERSION_MINOR=$llvm_version_minor",
     "LLVM_VERSION_PATCH=$llvm_version_patch",
     "LLVM_WITH_Z3=",
     "PACKAGE_VERSION=${llvm_version}git",
   ]
 
+  if (llvm_build_native) {
+    values += [
+      "LLVM_NATIVE_ASMPARSER=1",
+      "LLVM_NATIVE_ASMPRINTER=1",
+      "LLVM_NATIVE_DISASSEMBLER=1",
+      "LLVM_NATIVE_TARGET=1",
+      "LLVM_NATIVE_TARGETINFO=1",
+      "LLVM_NATIVE_TARGETMC=1",
+      "LLVM_NATIVE_TARGETMCA=1",
+    ]
+  } else {
+    values += [
+      "LLVM_NATIVE_ASMPARSER=",
+      "LLVM_NATIVE_ASMPRINTER=",
+      "LLVM_NATIVE_DISASSEMBLER=",
+      "LLVM_NATIVE_TARGET=",
+      "LLVM_NATIVE_TARGETINFO=",
+      "LLVM_NATIVE_TARGETMC=",
+      "LLVM_NATIVE_TARGETMCA=",
+    ]
+  }
+
   if (current_os == "win") {
     values += [
       "HAVE_SYSEXITS_H=",
       "LLVM_ON_UNIX=",
     ]
   } else {
     values += [
       "HAVE_SYSEXITS_H=1",

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

llvm_all_targets = [
   "PowerPC",
   "RISCV",
   "Sparc",
   "SystemZ",
   "WebAssembly",
   "X86",
 ]
 
-if (llvm_targets_to_build == "host") {
-  if (host_cpu == "arm64") {
-    llvm_targets_to_build = [ "AArch64" ]
-  } else if (host_cpu == "arm") {
-    llvm_targets_to_build = [ "ARM" ]
-  } else if (host_cpu == "ppc" || host_cpu == "ppc64") {
-    llvm_targets_to_build = [ "PowerPC" ]
-  } else if (host_cpu == "x86" || host_cpu == "x64") {
-    llvm_targets_to_build = [ "X86" ]
-  } else {
-    assert(false, "add your host_cpu above")
-  }
+# FIXME: This should be based off target_cpu once cross compiles work.
+  native_target = "AArch64"
+  native_target = "ARM"
+  native_target = "PowerPC"
+  native_target = "X86"
+
+if (llvm_targets_to_build == "host") {
+  llvm_targets_to_build = [ native_target ]
 } else if (llvm_targets_to_build == "all") {
   llvm_targets_to_build = llvm_all_targets
 }
 
 # Validate that llvm_targets_to_build is set to a list of valid targets,
 # and remember which targets are built where needed (for conditionally-built
 # unittest targets).
 llvm_build_AArch64 = false
 llvm_build_AMDGPU = false
 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
+llvm_build_native = false
 foreach(target, llvm_targets_to_build) {
+  if (target == native_target) {
+    llvm_build_native = true
+  }
   if (target == "AArch64") {
     llvm_build_AArch64 = true
   } else if (target == "AMDGPU") {
     llvm_build_AMDGPU = true
   } else if (target == "ARM") {
     llvm_build_ARM = true
   } else if (target == "BPF") {
     llvm_build_BPF = true
if (target == "AArch64") {
     foreach(target, llvm_all_targets) {
       all_targets_string += "$0x0a    " + target
     }
     assert(false, "Unknown target '$target' in llvm_targets_to_build. " +
                       "Known targets:" + all_targets_string)
   }
 }
 
-# FIXME: This should be based off target_cpu once cross compiles work.
-if (host_cpu == "arm64") {
-  native_target = "AArch64"
-} else if (host_cpu == "arm") {
-  native_target = "ARM"
-} else if (host_cpu == "ppc" || host_cpu == "ppc64") {
-  native_target = "PowerPC"
-} else if (host_cpu == "x86" || host_cpu == "x64") {
-  native_target = "X86"
-} else {
-  assert(false, "Unsuppored host_cpu '$host_cpu'.")
-}
-
 supported_android_toolchains = []
 
 if (android_ndk_path != "") {
   if (llvm_build_AArch64) {
     supported_android_toolchains +=
         [ "//llvm/utils/gn/build/toolchain:stage2_android_aarch64" ]
   }
   if (llvm_build_ARM) {
     supported_android_toolchains +=
         [ "//llvm/utils/gn/build/toolchain:stage2_android_arm" ]
   }
 }