Fails to build on 32-bit x86

x86_abi_support.asm only defines ARCH_X86_64 but EbDefinitions.h adds __i386__ to ARCH_X86. However, assembly isn't built if uname -m returns i386 or i686.

From error log:

ld: error: Bin/Release/libSvtAv1Enc.so.0.8.1: undefined reference to Log2f_SSE2
ld: error: Bin/Release/libSvtAv1Enc.so.0.8.1: undefined reference to aom_blend_a64_hmask_sse4_1
ld: error: Bin/Release/libSvtAv1Enc.so.0.8.1: undefined reference to aom_blend_a64_mask_avx2

From error log after applying fe54f0274277:

Source/Lib/Common/ASM_SSE2/aom_subpixel_8t_sse2.asm:204: error: impossible combination of address sizes
Source/Lib/Common/ASM_SSE2/x86_abi_support.asm:237: ... from macro `ALIGN_STACK' defined here
Source/Lib/Common/ASM_SSE2/aom_subpixel_8t_sse2.asm:213: error: impossible combination of address sizes
Source/Lib/Common/ASM_SSE2/aom_subpixel_8t_sse2.asm:21: ... from macro `GET_FILTERS_4' defined here