Use `extern` where appropriate so that we can remove `-fcommon`
on macOS and others.  On macOS, `-fcommon` generates a number of
linker warnings.

I've tested building on macOS, Linux, FreeBSD, NetBSD, OpenBSD
and illumos.  I am not in a position to test on AIX or other
more esoteric platforms, however.

Remote whitespace at the ends of lines.
Remove blank lines from the ends of files.
Change modes on source files so that they
are not executable.

Signed-off-by: Dan Cross <cross@gajendra.net>

input, and unicode output, which have been broken due
to the change of the size of Rune from two bytes to
four bytes.

(Unicode-le and unicode-be output have not been
affected, since they work different, and produce
correct output as long as sizeof(Rune) >= 2.)

In all of the affected functions an extra array of N
elements of type u16int is used to temporarily store
the 16-bit unicode data.  As this increases stack
usage, perhaps a different, slightly more complicated
solution might be preferred, where only a single
`Rune buf[N]' is used for both temporary storage and
the result.

R=rsc
CC=codebot
http://codereview.appspot.com/1574041

2126 -> 03a9 # greek capital letter omega
2012 -> 201c # left double quotation mark
00a4 -> 20ac # euro sign
f7ff -> f8ff # apple logo

R=rsc
CC=codebot
http://codereview.appspot.com/1233043

http://codereview.appspot.com/117063