Test: Compile doh_ffi_test for both architectures and append 32/64 suffixes

As DoH coverage test builds 64-bit doh_ffi_test and run it on a
32-bit device, we compile both 32-bit and 64-bit doh_ffi_test so
TestFilePushSetup can find the file path.

Bug: 243253532
Bug: 237767883
Test: atest doh_ffi_test
Change-Id: I4fff58feae0b3342ec62986af22496b36734edfa