Configure script: drop --with-caf, add -D option

configure

@@ -83,8 +83,6 @@ Usage: $0 [OPTION]... [VAR=VALUE]...
     --with-bison=PATH      path to bison executable
     --with-broker=PATH     path to Broker install root
                            (Zeek uses an embedded version by default)
-    --with-caf=PATH        path to C++ Actor Framework install root
-                           (a Broker dependency that is embedded by default)
     --with-gen-zam=PATH    path to Gen-ZAM code generator
                            (Zeek uses an embedded version by default)
     --with-flex=PATH       path to flex executable
@@ -116,6 +114,9 @@ Usage: $0 [OPTION]... [VAR=VALUE]...
 
     --display-cmake        don't create build configuration, just output final CMake invocation
 
+  Advanced Options (for developers):
+    -D PARAM               passes a parameter directly to CMake
+
   Influential Environment Variables (only on first invocation
   per build directory):
     CC                     C compiler command
@@ -195,6 +196,14 @@ while [ $# -ne 0 ]; do
             echo "${usage}" 1>&2
             exit 1
             ;;
+        -D)
+            shift
+            if [ $# -eq 0 ]; then
+                echo "Error: -D requires an argument."
+                exit 1
+            fi
+            CMakeCacheEntries="$CMakeCacheEntries -D $1"
+            ;;
         --cmake=*)
             CMakeCommand=$optarg
             ;;