unix: add checksparse.sh script
unix: remove unused function uv__strlcpy()
unix: fix up function prototypes in signal.c
unix: make uv__work_cancel() static
unix: make uv__read_start_common() static
unix: fix include in cygwin.c
unix: fix up #if defined checks

`#if FOO` (where FOO is undefined) is a legal construct in C89 and C99
but gcc, clang and sparse complain loudly about it at higher warning
levels.

Squelch those warnings. Makes the code more consistent as well.
unix, windows: ANSI-fy uv_tty_reset_mode() prototype
linux: fix race in uv_resident_set_memory()

uv_resident_set_memory() used a global buffer to read data into, which
is a decidedly unsafe thing to do in a multi-threaded environment.
test, bench: ANSI-fy function prototypes

Replace `void f()` with `void f(void)`; the former means "a function
that takes any number of arguments, including none" while the latter
is what is actually intended: a function taking no arguments.

The first form also isn't strictly conforming ANSI/ISO C.
test, bench: make functions/variables static

Make functions and variables that are local to the compilation unit
static. Remove what turns out to be unused.
test: remove unused function declaration
test: simplify tcp_ref2b

Said test doesn't need its own close callback, it can piggyback on the
common close callback.
test: fix #if defined checks

Same as edd1007 but this time for the tests.