Fix issue with "reboot doesn't work on 32-bit targets"

With the introduction of GLIBC v2.34, all 32-bit devices running Linux
get the option of having a 64-bit time_t to survice the UNIX 2038
apocalypse.

Support for 64-bit time_t was added to libuev in v2.4.0.  The build
flags for linking against libuev are defined in the library's .pc
files, which basically gives you -D_TIME_BITS=64 for your CPPFLAGS.

However, it turns out the $(uev_CFLAGS) from pkg-config were only used
when building the main finit binary -- not for the plugins, causing
some really wacky behavior as a result.  All plugins and Finit itself
had some very different opinions on what `struct plugin` looked like,
including offsets and size.  This led to all I/O plugins initializing
their sockets at the wrong offset -- little-endian 32-bit targets set
the HOOK_SHUTDOWN callback hook to address 0x1 -- which the reboot
code then tried to execute, of course leading to a segfault.

This is quite possibly the root cause of issue #216

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

plugins/Makefile.am

@@ -3,7 +3,7 @@ AM_LDFLAGS          = -module -avoid-version -shared
 AM_CFLAGS           = -W -Wall -Wextra -Wno-unused-parameter -std=gnu99
 AM_CPPFLAGS         = -I$(top_srcdir)/src -U_FORTIFY_SOURCE
 AM_CPPFLAGS        += -D_XOPEN_SOURCE=600 -D_BSD_SOURCE -D_GNU_SOURCE -D_DEFAULT_SOURCE
-AM_CPPFLAGS        += $(lite_CFLAGS)
+AM_CPPFLAGS        += $(lite_CFLAGS) $(uev_CFLAGS)
 
 if STATIC
 noinst_LTLIBRARIES  = libplug.la