Fix weak/strong attribute of __errno_location and it's __GI alias

libc internal users need strong __GI___errno_location alias,
but __errno_location itself needs to be weak to avoid multiple refs when
static linking with other libs (libpthread) containg their own ver of
same symbol.

arc-linux-uclibc-nm libc/misc/internals/__errno_location.o

Before Mischa's changes
[_stdio_init() referred to NULL alias - static bbox crashed]

00000000 W __GI___errno_location
00000000 T __errno_location

--------------------------------------------
After Mischa's Fix
[Fixed static bbox crash, but __errno_location non-weak, so redef with
libpthread]

00000000 T __GI___errno_location
00000000 T __errno_location

--------------------------------------------
After Today's fix

00000000 T __GI___errno_location
00000000 W __errno_location

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>