[gn] Fix targets for x86 v8_target_arch

Those were wrongly translated from gyp with ia32. This should
land before renaming v8_target_arch to v8_target_cpu.

BUG=chromium:620527
NOTRY=true
TBR=vogelheim@chromium.org

Review-Url: https://codereview.chromium.org/2065323004
Cr-Commit-Position: refs/heads/master@{#37027}

test/cctest/BUILD.gn

@@ -194,7 +194,7 @@ v8_executable("cctest") {
       "test-run-wasm-relocation-arm64.cc",
       "test-utils-arm64.cc",
     ]
-  } else if (v8_target_arch == "ia32") {
+  } else if (v8_target_arch == "x86") {
     sources += [
       "test-assembler-ia32.cc",
       "test-code-stubs-ia32.cc",

test/unittests/BUILD.gn

@@ -122,7 +122,7 @@ v8_executable("unittests") {
     sources += [ "compiler/arm/instruction-selector-arm-unittest.cc" ]
   } else if (v8_target_arch == "arm64") {
     sources += [ "compiler/arm64/instruction-selector-arm64-unittest.cc" ]
-  } else if (v8_target_arch == "ia32") {
+  } else if (v8_target_arch == "x86") {
     sources += [ "compiler/ia32/instruction-selector-ia32-unittest.cc" ]
   } else if (v8_target_arch == "mips" || v8_target_arch == "mipsel") {
     sources += [ "compiler/mips/instruction-selector-mips-unittest.cc" ]