dist/tools/avarice: Detect GDB automatically

While some users likely still use avr-gdb, more and more systems are starting
to use gdb-multiarch. In order to work in both cases, the script now just
checks which version is installed. (If both are installed, gdb-multiarch is
preferred.)

dist/tools/avarice/debug.sh

@@ -3,9 +3,18 @@
 # The setsid command is needed so that Ctrl+C in GDB doesn't kill avarice
 : ${SETSID:=setsid}
 
+if gdb-multiarch -v > /dev/null; then
+    GDB=gdb-multiarch
+elif avr-gdb -v > /dev/null; then
+    GDB=avr-gdb
+else
+    echo "Couldn't find multiarch GDB or AVR GDB. Check \$PATH."
+    exit 1
+fi
+
 sleep 2
 ${SETSID} -w avarice $1 &
-sleep 3 && avr-gdb -ex "target remote localhost:$3" $4
+sleep 3 && $GDB -ex "target remote localhost:$3" $4
 
 # avarice exits with 1 if the connection is released, therefore we always exit with 0
 exit 0