std.tar: implement executable_bit_only mode

[andrewrk]

zig/lib/std/tar.zig

Lines 180 to 187 in 3a47bc7

	.executable_bit_only => {
	// This code does not look at the mode bits yet. To implement this feature,
	// the implementation must be adjusted to look at the mode, and check the
	// user executable bit, then call fchmod on newly created files when
	// the executable bit is supposed to be set.
	// It also needs to properly deal with ACLs on Windows.
	@panic("TODO: unimplemented: tar ModeMode.executable_bit_only");
	},

Related:

• std.tar: copy another project's full test suite and make them all pass #14310

[andrewrk]

The idea of doing anything on Windows with the executable bit in pipeToFileSystem can be a separate issue. This can be closed if there is added an option that is defined to honor the executable bit on posix systems and do nothing on Windows systems.

This is also a low priority issue now because of the plan outlined here: #17463 (comment)