Use libc_hidden_* for strtoumax (bug 15105).

Use libc_hidden_* for strtoumax (bug 15105).

On sparc, localplt test failures appear when building with -Os because
of a call to strtoumax from
sysdeps/unix/sysv/linux/sparc/sparc64/get_clockfreq.c, and strtoumax
is not inlined when building with -Os.  This patch fixes those
failures by using libc_hidden_proto and libc_hidden_def for strtoumax.

Tested with build-many-glibcs.py for
sparc64-linux-gnu-disable-multi-arch, sparc64-linux-gnu,
sparcv9-linux-gnu-disable-multi-arch, sparcv9-linux-gnu that this
fixes that test failure with -Os.

	[BZ #15105]
	* sysdeps/wordsize-32/strtoumax.c (strtoumax): Use
	libc_hidden_def.
	* sysdeps/wordsize-64/strtoumax.c (strtoumax): Likewise.
	* include/inttypes.h: New file.