Fix -Os putc_unlocked, fputc_unlocked linknamespace, localplt issues (bug 15105,...

Fix -Os putc_unlocked, fputc_unlocked linknamespace, localplt issues (bug 15105, bug 19463).

Continuing the fixes for linknamespace and localplt test failures with
-Os that arise from functions not being inlined in that case, this
patch fixes such failures for putc_unlocked and fputc_unlocked.

libc_hidden_* are used for both functions, while namespace issues are
addressed by making putc_unlocked a weak alias of hidden
__putc_unlocked, which is called in the one place where namespace
issues arise (and defined as an inline function in include/stdio.h).

Tested for x86_64 (both without -Os to make sure that case continues
to work, and with -Os to make sure all the relevant linknamespace and
localplt test failures are resolved).  This completes fixing the -Os
linknamespace failures (at least for x86_64); localplt failures remain
after this patch.

2018-02-19  Joseph Myers  <joseph@codesourcery.com>

	[BZ #15105]
	[BZ #19463]
	* libio/fputc_u.c (fputc_unlocked): Use libc_hidden_def.
	* libio/putc_u.c (putc_unlocked): Rename to __putc_unlocked and
	define as weak alias of __putc_unlocked.  Use libc_hidden_weak.
	* include/stdio.h [!_ISOMAC] (fputc_unlocked): Use
	libc_hidden_proto.
	[!_ISOMAC] (putc_unlocked): Likewise.
	[!_ISOMAC] (__putc_unlocked): Declare as hidden function, and
	define inline if [__USE_EXTERN_INLINES].
	* misc/syslog.c (__vsyslog_chk): Call __putc_unlocked instead of
	putc_unlocked.