As a result of https://codereview.chromium.org/2116183002/ if we specify a custom v8_target_cpu and not custom_toolchain, v8 is compiled twice.

E.g. specify:
target_cpu = "x86"
v8_target_cpu = "arm"

The resulting output folder has a clang_x86_v8_arm that includes mksnapshot. The other executables, e.g. d8 are in the main output folder. Both folders have subfolders with all the objects. Also the number of ninja tasks nearly doubled (not sure if they're deduped through goma on-the-fly).

Now lets add:
custom_toolchain = "//build/toolchain/linux:clang_x86_v8_arm"

Now everything is as before (in gyp). All executables are in the main output folder.

---

If this behavior can't be fixed, I'd at least suggest an assertion requiring explicit custom_toolchain to avoid the double compilation.