clang build buggy code with certain CPUTYPE setting

Dear list,

I have done a few builds of CURRENT in a row one or two weeks apart. The
builds with CPUTYPE?=amdfam10 set produce buggy code, for example while
running mergemaster I get this error:

PLEASE submit a bug report to https://bugs.freebsd.org/submit/ and
include the crash backtrace, preprocessed source, and associated run
script.
Stack dump:
0.      Program arguments: cc --version 
#0 0x00000000040ede6e (/usr/bin/cc+0x40ede6e)
#1 0x00000000040ec0e5 (/usr/bin/cc+0x40ec0e5)
#2 0x00000000040ee550 (/usr/bin/cc+0x40ee550)
#3 0x000000080553babe (/lib/libthr.so.3+0x19abe)
Illegal instruction
make: "/usr/src/share/mk/bsd.compiler.mk" line 181: Unable to determine
compiler type for CC=cc.  Consider setting COMPILER_TYPE.

The 13-CURRENT world built without CPUTYPE runs fine, the same for
recent 12.2-STABLE world build with CPUTYPE?=amdfam10 on the same
machine.

Any tips would be appreciated,

--  
Marek Zarychta