Enable compressed debug on little-endian targets

Enable compressed debug on little-endian targets

Compressed debug was enabled by default in commit c910570e7573, but
broke the build on big-endian targets, and so was disabled in
89ed2ecb14ce.

Older versions of LLD fail with big-endian compressed debug sections.
This was fixed in LLD upstream (commit c6ebc651b6fa) and merged to
FreeBSD main (commit d69d07569ee2) by dim.

External toolchains (e.g. the llvm12 package) will not yet have the fix.
These may be used to link against base system .a archives, so compressed
debug sections would cause trouble even though the base system is fixed.

Enable compressed debug sections again, for little-endian targets only.
As discussed on freebsd-hackers[1] I expect to undo this in the future
(using compressed debug everywhere), once fixed versions of lld are
widely available.

Note that to be pedantically correct we should check both the compiler
and the linker for compressed debug support, but given the external
toolchain constraint the extra complexity does not seem worthwhile.

[1] https://lists.freebsd.org/archives/freebsd-hackers/2021-August/000188.html

PR:		257638
Reported by:	jrtc27 [impact of .a archives]
Discussed with:	imp
Relnotes:	Yes
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D31454

Revert "Disable compressed debug by default"

This reverts commit 89ed2ecb14ceabc27883282cf96559a9e7d52717.