[PATCH, i386, AVX] Fix compress test.

[Kirill Yukhin]

Hello,

For 32-bit mode there's no __popcnt64 instruction,
so replace number of set bit calculation in 64b mask with two
invocations of _popcnt32.

Test started to pass for me under SDE.

gcc/testsuite/
        * gcc.target/i386/avx512f-vpcompressb-2.c: Fix popcnt for 32-bit mode.

Checked into main trunk.

--
Thanks, K