On the LKGR waterfall (and maybe elsewhere?) we have bots that do 32-bit x86 builds, but build with 32-bit arm v8.

This seems to not work in gn builds, here's a broken build after flipping these bots to gn:
https://build.chromium.org/p/chromium.lkgr/builders/ASan%20Debug%20%2832-bit%20x86%20with%20V8-ARM%29/builds/2477/steps/compile/logs/stdio

FAILED: clang_x64/obj/v8/v8_base/strings-storage.o 
/mnt/data/b/build/slave/cache/cipd/goma/gomacc ../../third_party/llvm-build/Release+Asserts/bin/clang++ -MMD -MF clang_x64/obj/v8/v8_base/strings-storage.o.d -DV8_DEPRECATION_WARNINGS -DENABLE_MDNS=1 -DENABLE_NOTIFICATIONS -DENABLE_PEPPER_CDMS -DENABLE_PLUGINS=1 -DENABLE_PDF=1 -DENABLE_PRINTING=1 -DENABLE_BASIC_PRINTING=1 -DENABLE_PRINT_PREVIEW=1 -DENABLE_SPELLCHECK=1 -DUSE_UDEV -DUI_COMPOSITOR_IMAGE_TRANSPORT -DUSE_AURA=1 -DUSE_PANGO=1 -DUSE_CAIRO=1 -DUSE_CLIPBOARD_AURAX11=1 -DUSE_DEFAULT_RENDER_THEME=1 -DUSE_GLIB=1 -DUSE_NSS_CERTS=1 -DUSE_X11=1 -DENABLE_WEBRTC=1 -DDISABLE_NACL -DENABLE_EXTENSIONS=1 -DENABLE_TASK_MANAGER=1 -DENABLE_THEMES=1 -DENABLE_CAPTIVE_PORTAL_DETECTION=1 -DENABLE_SESSION_SERVICE=1 -DENABLE_SUPERVISED_USERS=1 -DENABLE_SERVICE_DISCOVERY=1 -DFULL_SAFE_BROWSING -DSAFE_BROWSING_CSD -DSAFE_BROWSING_DB_LOCAL -DCHROMIUM_BUILD -DENABLE_MEDIA_ROUTER=1 -DFIELDTRIAL_TESTING_ENABLED -DCR_CLANG_REVISION=270823-1 -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -DCOMPONENT_BUILD -D_DEBUG -DDYNAMIC_ANNOTATIONS_ENABLED=1 -DWTF_USE_DYNAMIC_ANNOTATIONS=1 -D_GLIBCXX_DEBUG=1 -DV8_SHARED -DBUILDING_V8_SHARED -DVERIFY_HEAP -DV8_I18N_SUPPORT -DENABLE_HANDLE_ZAPPING -DV8_USE_EXTERNAL_STARTUP_DATA -DV8_TARGET_ARCH_IA32 -DENABLE_DISASSEMBLER -DV8_ENABLE_CHECKS -DOBJECT_PRINT -DVERIFY_HEAP -DDEBUG -DTRACE_MAPS -DU_USING_ICU_NAMESPACE=0 -DU_ENABLE_DYLOAD=0 -DU_NOEXCEPT= -DICU_UTIL_DATA_IMPL=ICU_UTIL_DATA_FILE -I../.. -Iclang_x64/gen -I../../v8 -I../../v8/include -I../../third_party/icu/source/common -I../../third_party/icu/source/i18n -fno-strict-aliasing --param=ssp-buffer-size=4 -fstack-protector -funwind-tables -fPIC -pipe -B../../third_party/binutils/Linux_x64/Release/bin -fcolor-diagnostics -fdebug-prefix-map=/mnt/data/b/build/slave/ASan_Debug__32-bit_x86_with_V8-ARM_/build/src=. -pthread -m64 -march=x86-64 -g2 -gsplit-dwarf --sysroot=../../build/linux/debian_wheezy_amd64-sysroot -fvisibility=hidden -Xclang -load -Xclang ../../third_party/llvm-build/Release+Asserts/lib/libFindBadConstructs.so -Xclang -add-plugin -Xclang find-bad-constructs -Xclang -plugin-arg-find-bad-constructs -Xclang check-templates -Xclang -plugin-arg-find-bad-constructs -Xclang follow-macro-expansion -Xclang -plugin-arg-find-bad-constructs -Xclang check-implicit-copy-ctors -Xclang -plugin-arg-find-bad-constructs -Xclang check-ipc -Wheader-hygiene -Wstring-conversion -Werror -Wall -Wno-unused-variable -Wno-missing-field-initializers -Wno-unused-parameter -Wno-c++11-narrowing -Wno-covered-switch-default -Wno-deprecated-register -Wno-unneeded-internal-declaration -Wno-inconsistent-missing-override -Wno-shift-negative-value -Wno-undefined-var-template -O2 -fno-ident -fdata-sections -ffunction-sections -fno-threadsafe-statics -fvisibility-inlines-hidden -Wno-undefined-bool-conversion -Wno-tautological-undefined-compare -std=gnu++11 -fno-rtti -fno-exceptions -Wno-deprecated -c ../../v8/src/profiler/strings-storage.cc -o clang_x64/obj/v8/v8_base/strings-storage.o
In file included from ../../v8/src/profiler/strings-storage.cc:5:
In file included from ../../v8/src/profiler/strings-storage.h:8:
In file included from ../../v8/src/allocation.h:8:
In file included from ../../v8/src/globals.h:13:
../../v8/src/base/build_config.h:145:2: error: Target architecture ia32 is only supported on ia32 host
#error Target architecture ia32 is only supported on ia32 host
 ^
1 error generated.


I'll take a look, but I know nothing about this build config, so if someone wants to offer hints: I'll take them.