The phase is added instead of the try_files phase.  Unlike the old phase, the
new one supports registering multiple handlers.  The try_files implementation is
moved to a separate ngx_http_try_files_module, which now registers a precontent
phase handler.

The http_rewrite module cannot be selected when http is disabled.
Fixed the PCRE check condition to avoid irrelevant check failure.
This is a regression from 4d874b4d82ed.

Signed-off-by: Samuel Martin <s.martin49@gmail.com>

On Cygwin and NetBSD 7.0+ struct in_pktinfo has no ipi_spec_dst field, which
caused nginx compilation error.  Now presence of this field is ensured by the
IP_PKTINFO feature test.

The problem was introduced by dbb0c854e308 (1.13.0).

The sched_setaffinity() function was introduced in DragonFly BSD 4.7,
so it is no longer Linux-specific.

Prodded by Sepherosa Ziehau.

Oracle Developer Studio 12.5 introduced GCC-compatible __sync builtins.
Unfortunately, these builtins are neither GCC-compatible (they generate
warnings when used with volatile), nor working (unexpectedly fail on
unpredictable combinations of code layout and compiler flags).  As such,
the gcc builtin atomic operations configure test explicitly disabled when
compiling with Sun C.