QEMU's code relies on left shifts of signed integers always
being defined behaviour with the obvious 2s-complement
semantics. The only way to tell the compiler (and any
associated undefined-behaviour sanitizer) that we require a
C dialect with these semantics is to use the -fwrapv option.
This is a bit of a heavy hammer for the job as it also gives
us guaranteed semantics on integer arithmetic overflow which
in theory we don't require.
In an ideal world this would allow us to drop the warning
flag -Wno-shift-negative-value, but we must retain this to
avoid spurious warnings on clang versions predating the
fix to https://llvm.org/bugs/show_bug.cgi?id=25552.
Backports commit 2d31515bc0880a1cea86ce638d2a109f4f4e6f7d from qemu
MinGW seems to compile currently without warnings, so it should
be safe to enable -Werror now for this environment, too.
Backports commit e4650c81b3d15ba67236815defbb475c4bdf8690 from qemu
This fixes these warnings from shellcheck:
^-- SC2006: Use $(..) instead of deprecated `..`
Backports commit 89138857619b2a023c32200e9af780792ccaa8c3 from qemu