Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r245133:
Only assign the environ in the startup code when environ is NULL.

Note that this is not the merge, but a reimplementation of the fix,
done for the not-consolidated code in the stable/9.

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Whitespace nit

Use default WARNS setting (of 6) for lib/csu.

PR: bin/140089
Reviewed by: jmallett
Approved by: ed (co-mentor)

Properly declare non-extern functions in crt1

Also move the declarations after __progname consistently to
make the distinction clearer.

Reviewed by: jmallett
Approved by: ed (co-mentor)

__main and __gccmain are no longer required, so eliminate them.

Submitted by: jmallet@

Bring C runtime bits for FreeBSD/mips from p4 mips2-jnpr branch.

Approved by: cognet (mentor)