If the newlib .info files are installed using install-info, 'info libc' and
'info libm' don't work.
This seems to be due to the formatting of the directory entry line not being
quite right, so fix that.
Also use @direntry texinfo command, rather than writing .info directory entry
literally.
Also use @dircategory texinfo command to place into 'Newlib' category, rather
than ending up in 'Miscellaneous'
newlib/ChangeLog:
2015-03-13 Jon TURNEY <jon.turney@dronecode.org.uk>
* libc/libc.texinfo: Fix directory entry.
* libm/libm.texinfo: Ditto.
Signed-off-by: Jon TURNEY <jon.turney@dronecode.org.uk>