Fix x86 build with msvc compiler

[pps83]

Replace check for _M_X64 with _M_IX86 to make sure x86 builds can be compiled

[pps83]

after pulling latest I got tons of compilation errors:

1>FastPFor\headers\simdbitpacking.h(14,48): error C2061: syntax error: identifier '__m128i'
1>(compiling source file '../src/coders.cpp')
1>FastPFor\headers\simdbitpacking.h(17,26): error C2061: syntax error: identifier '__m128i'
1>(compiling source file '../src/coders.cpp')
1>FastPFor\headers\simdbitpacking.h(18,31): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>(compiling source file '../src/coders.cpp')
1>FastPFor\headers\simdbitpacking.h(18,31): error C2143: syntax error: missing ',' before '*'

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