Fix make check on OmniOS

Fix make check on OmniOS

We need the defines from config.h before
we include <testing.h>, or we get the following error on OmniOS:

make  test_common test_meta_data  test_utils_avltree test_utils_heap  test_utils_time test_utils_subst
gcc -DHAVE_CONFIG_H -I. -I../../src  -I../../src -DPREFIX='"/opt/collectd"'  -DCONFIGFILE='"/opt/collectd/etc/collectd.conf"'  -DLOCALSTATEDIR='"/opt/collectd/var"'  -DPKGLOCALSTATEDIR='"/opt/collectd/var/lib/collectd"'  -DPIDFILE='"/opt/collectd/var/run/collectd.pid"' -DPLUGINDIR='"/opt/collectd/lib/collectd"'  -DPKGDATADIR='"/opt/collectd/share/collectd"'   -Wall -Werror -g -O2 -c -o common_test.o common_test.c
In file included from collectd.h:31:0,
                 from common.h:31,
                 from common_test.c:28:
../../src/config.h:1631:0: error: "_FILE_OFFSET_BITS" redefined [-Werror]
 #define _FILE_OFFSET_BITS 64
 ^
In file included from /usr/include/inttypes.h:41:0,
                 from ../../src/testing.h:30,
                 from common_test.c:27:
/opt/gcc-5.1.0/lib/gcc/i386-pc-solaris2.11/5.1.0/include-fixed/sys/feature_tests.h:231:0: note: this is the location of the previous definition
 #define _FILE_OFFSET_BITS 32
 ^
cc1: all warnings being treated as errors
*** Error code 1
make: Fatal error: Command failed for target `common_test.o'