Add advanced build option to omit building plugins

Compiling the plugins takes quite a long time and is unnecessary
if you're only working on the core code. Having an option is nicer
than having to edit the configure script by hand.

Change-Id: I401867355d897ce3fd899d9daf25ea9afcc380f0

tools/configure

@@ -935,7 +935,7 @@ whichadvanced () {
     echo ""
     printf "Enter your developer options (press only enter when done)\n\
 (D)EBUG, (L)ogf, Boot(c)hart, (S)imulator, (P)rofiling, (V)oice, (U)SB Serial, (W)in32 crosscompile,\n\
-Win(6)4 crosscompile, (T)est plugins, S(m)all C lib, Logf to Ser(i)al port:"
+Win(6)4 crosscompile, (T)est plugins, (O)mit plugins, S(m)all C lib, Logf to Ser(i)al port:"
     if [ "$modelname" = "iaudiom5" ]; then
       printf ", (F)M radio MOD"
     fi
@@ -975,6 +975,10 @@ Win(6)4 crosscompile, (T)est plugins, S(m)all C lib, Logf to Ser(i)al port:"
         echo "Including test plugins"
         extradefines="$extradefines -DHAVE_TEST_PLUGINS"
         ;;
+      [Oo])
+        echo "Disabling building of plugins"
+        plugins="no"
+        ;;
       [Cc])
         echo "bootchart enabled (logf also enabled)"
         bootchart="yes"