Don't error out in install-wrappers.sh if some binary tools are missing

If installing on top of a prebuilt win32 release of llvm instead of
building from source, the nm and strings executables are missing,
and MSYS2 errors out when creating a symlink to a file that doesn't
exist (since it does a copy instead of making an actual symlink).

install-wrappers.sh

@@ -18,7 +18,7 @@ for arch in $ARCHS; do
         ln -sf clang-target-wrapper.sh $arch-w64-mingw32-$exec
     done
     for exec in ar ranlib nm strings; do
-        ln -sf llvm-$exec $arch-w64-mingw32-$exec
+        ln -sf llvm-$exec $arch-w64-mingw32-$exec || true
     done
     for exec in strip; do
         ln -sf $(which true) $arch-w64-mingw32-$exec