add mips long_call attribute

[James E Wilson <wilson at specifix dot com>]

A customer wants to be able to specify that some functions must be long
calls.  Currently, the only way to do this is the -mlong-calls option
which forces all calls to be long calls.  This is overkill.  We can get
the desired result by adding an attribute long_call that does the same
thing as the -mlong-calls option, except one function at a time.  The
ARM and RS6000 ports already have similar attributes.

I have tested this with a mips-elf C and C++ cross compiler build and
make check.  There were no regressions.  I also tested the doc change
with make info and make dvi.

I'll wait a few days in case a MIPS maintainer wants to comment, then I
plan to check it in.
-- 
Jim Wilson, GNU Tools Support, http://www.specifix.com

Attachment: patch.long-call.attr
Description: Text document