Fix exception handing on WSL

[sobolevsv]

This fix makes libunwind working on Windows Subsystem for Linux.
#ClickHouse/ClickHouse#6480

syscall mincore on WSL return -1 and breaks exception handing.
I think it is a bad idea to make a syscall while unwinding stack.
compiling with libstdc++(option USE_LIBCXX) also makes clickhouse working on WSL.

[alexey-milovidov]

We cannot avoid this type of hack. Otherwise we will get segfault during asynchronous unwiding.
It's possible to do some workaround instead.

[alexey-milovidov]

See also:

1. https://github.com/libunwind/libunwind/blob/49d2bf0e55c1b4ff90371e8e6fd9ac88c3d26834/src/x86_64/Ginit.c#L150
2. https://github.com/gperftools/gperftools/blob/master/src/stacktrace_x86-inl.h#L262

[alexey-milovidov]

Please tell what is the value of errno after this call on WSL?

[alexey-milovidov]

We can modify our check that if the errno is not EFAULT then proceed.

[sobolevsv]

thank you for a hint to check errno! mincore is not implemented on WSL, errno = 38
please see my quickest workaround :)

[alexey-milovidov]

Ok.