AppVeyor msys2 build broken

[vincentkfu]

AppVeyor recently upgraded their Visual Studio 2019 worker image.

Since the upgrade our Windows build using the msys2 toolchain is broken.

Good build with previous image: https://ci.appveyor.com/project/vincentkfu/fio/builds/46790123/job/lktpna0v91260rko
Bad build with current image: https://ci.appveyor.com/project/vincentkfu/fio/builds/46792337/job/rb3neloe6bn66t0r

Here is the error:

    CC unittests/oslib/strcasestr.o
    CC unittests/oslib/strsep.o
  LINK fio
ld.lld: error: undefined symbol: static_tv_valid
>>> referenced by gettime.o
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [Makefile:623: fio] Error 1

The definition of static_tv_valid is guarded by CONFIG_TLS_THREAD and ARCH_HAVE_CPU_CLOCK both of which should be defined for this platform.

For CONFIG_TLS_THREAD we have in the configure output:

socklen_t                     yes
__thread                      yes
RUSAGE_THREAD                 yes

For ARCH_HAVE_CPU_CLOCK we have in arch/arch-x86_64.h:

#define ARCH_HAVE_FFZ
#define ARCH_HAVE_SSE4_2
#define ARCH_HAVE_CPU_CLOCK

A possible cause is the change from clang 15.0.7-3 to 16.0.0-1 in the new worker image, although there is nothing obvious in the clang16 release notes.

[vincentkfu]

Rishabh Shukla investigated this and found the following:

• Using ld instead of lld produces a successful build
• Using -femulated-tls does not resolve the issue
• The clang 16 release notes mention a fix for code generation with emulated TLS

lld appears to be the source of the problem but we found no flags or options to get the build working with lld.

Here are three options

• disable __thread support
• switch from lld to ld
• use the previous AppVeyor worker image

Until there is a real fix let us work around this problem by disabling __thread support for AppVeyor msys2 builds.