tests: reset CFLAGS

* tests/run.in: Here.  This helps when spins is installed an the tests
actually compile code; we do not want to inherit the -std=c11
-fvisibility=hidden set for compiling Spot.

tests/run.in

@@ -48,6 +48,11 @@ test -z "$1" &&
     PYTHONPATH=$pypath DYLD_LIBRARY_PATH=$modpath exec $PREFIXCMD @PYTHON@
 srcdir="@srcdir@"
 
+# Reset CFLAGS, because some tests call the compiler, and we do not
+# want to inherit parameters likes -std=c11 -fvisibility=hidden
+CFLAGS=
+export CFLAGS
+
 case $1 in
     */*)
 	dir=${1%/*}