We need to adjust the script that runs the tests to get them out of the
build directory not the original source directory and we need to be able
to specify an alternate re2c binary when running system tests.

This patch should be sent upstream.

--- re2c-0.16/run_tests.sh.in.orig	2016-03-08 06:11:49.073497153 -0800
+++ re2c-0.16/run_tests.sh.in	2016-03-08 13:59:57.512468231 -0800
@@ -28,7 +28,7 @@
 skeleton=0
 keep_tmp_files=0
 wine=""
-re2c="./re2c"
+re2c="${RE2C_BIN:-@builddir@/re2c}"
 threads=`detect_cpu_count; echo $CPUS`
 tests=()
 for arg in $*
@@ -57,7 +57,7 @@
 test_srcdir=""
 if [ ${#tests[@]} -eq 0 ]
 then
-    test_srcdir="@top_srcdir@/test"
+    test_srcdir="./test"
     tests=(`find $test_srcdir -name '*.re' | sort`)
 fi
 test_blddir="test_"`date +%y%m%d%H%M%S`