Update GN build to use v8_target_cpu instead of v8_target_arch.

test/unittests/BUILD.gn

Index: test/unittests/BUILD.gn
diff --git a/test/unittests/BUILD.gn b/test/unittests/BUILD.gn
index 21ba5a1e9e6e3381878e8354d74d7ae2c6b3a5f8..85c1a485c7f16b1a6126b1f401d5b7584be23bcf 100644
--- a/test/unittests/BUILD.gn
+++ b/test/unittests/BUILD.gn
@@ -118,21 +118,21 @@ v8_executable("unittests") {
     "wasm/wasm-macro-gen-unittest.cc",
   ]
 
-  if (v8_target_arch == "arm") {
+  if (v8_target_cpu == "arm") {
     sources += [ "compiler/arm/instruction-selector-arm-unittest.cc" ]
-  } else if (v8_target_arch == "arm64") {
+  } else if (v8_target_cpu == "arm64") {
     sources += [ "compiler/arm64/instruction-selector-arm64-unittest.cc" ]
-  } else if (v8_target_arch == "x86") {
+  } else if (v8_target_cpu == "x86") {
     sources += [ "compiler/ia32/instruction-selector-ia32-unittest.cc" ]
-  } else if (v8_target_arch == "mips" || v8_target_arch == "mipsel") {
+  } else if (v8_target_cpu == "mips" || v8_target_cpu == "mipsel") {
     sources += [ "compiler/mips/instruction-selector-mips-unittest.cc" ]
-  } else if (v8_target_arch == "mips64" || v8_target_arch == "mips64el") {
+  } else if (v8_target_cpu == "mips64" || v8_target_cpu == "mips64el") {
     sources += [ "compiler/mips64/instruction-selector-mips64-unittest.cc" ]
-  } else if (v8_target_arch == "x64") {
+  } else if (v8_target_cpu == "x64") {
     sources += [ "compiler/x64/instruction-selector-x64-unittest.cc" ]
-  } else if (v8_target_arch == "ppc" || v8_target_arch == "ppc64") {
+  } else if (v8_target_cpu == "ppc" || v8_target_cpu == "ppc64") {
     sources += [ "compiler/ppc/instruction-selector-ppc-unittest.cc" ]
-  } else if (v8_target_arch == "s390" || v8_target_arch == "s390x") {
+  } else if (v8_target_cpu == "s390" || v8_target_cpu == "s390x") {
     sources += [ "compiler/s390/instruction-selector-s390-unittest.cc" ]
   }