Have built many previous versions of LibreSSL on the same system without issue, so it seems the offending commit was introduced in the last release.
$ make check
Making check in crypto
CCAS aes/aes-elf-x86_64.lo
CCAS aes/bsaes-elf-x86_64.lo
CCAS aes/vpaes-elf-x86_64.lo
aes/vpaes-elf-x86_64.s: Assembler messages:
aes/vpaes-elf-x86_64.s:172: Error: no such instruction: `palignr $12,%xmm5,%xmm5'
aes/vpaes-elf-x86_64.s:298: Error: no such instruction: `palignr $8,%xmm6,%xmm0'
aes/vpaes-elf-x86_64.s:436: Error: no such instruction: `palignr $15,%xmm8,%xmm1'
aes/vpaes-elf-x86_64.s:437: Error: no such instruction: `palignr $15,%xmm8,%xmm8'
aes/vpaes-elf-x86_64.s:442: Error: no such instruction: `palignr $1,%xmm0,%xmm0'
*** Error 1 in crypto (Makefile:7479 'aes/vpaes-elf-x86_64.lo': @echo " CCAS " aes/vpaes-elf-x86_64.lo;/bin/sh ../libtool --silent --...)
*** Error 1 in /usr/local/src/libressl-2.2.2 (Makefile:476 'check-recursive')
$ uname -a
OpenBSD <hostname> 5.7 GENERIC#2 amd64
$ dmesg|grep cpu
cpu0 at mainbus0: apid 0 (boot processor)
cpu0: Virtual CPU e7da7129d3ee, 3600.46 MHz
cpu0: FPU,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CFLUSH,MMX,FXSR,SSE,SSE2,HTT,SSE3,PCLMUL,SSSE3,FMA3,CX16,PCID,SSE4.1,SSE4.2,x2APIC,MOVBE,POPCNT,DEADLINE,AES,XSAVE,AVX,RDRAND,HV,NXE,LONG,LAHF,FSGSBASE,BMI1,HLE,AVX2,SMEP,BMI2,ERMS,INVPCID,RTM
cpu0: 64KB 64b/line 2-way I-cache, 64KB 64b/line 2-way D-cache, 512KB 64b/line 16-way L2 cache
cpu0: ITLB 255 4KB entries direct-mapped, 255 4MB entries direct-mapped
cpu0: DTLB 255 4KB entries direct-mapped, 255 4MB entries direct-mapped
cpu0: smt 0, core 0, package 0
cpu0: apic clock running at 1000MHz
acpicpu0 at acpi0