Add SKIPREADLINE support to make and cmake

It's mostly for headless support.
At the moment, for interactive uage without readline, some commands will exit the client prematurely if they use kbd_enter_pressed().

client/Makefile

@@ -256,11 +256,14 @@ LDLIBS += $(QTLDLIBS)
 CXXINCLUDES += $(QTINCLUDES)
 
 ## Readline
-ifeq ($(platform),Darwin)
-    LDLIBS += -L/usr/local/opt/readline/lib
-    INCLUDES += -I/usr/local/opt/readline/include
+ifneq ($(SKIPREADLINE),1)
+    ifeq ($(platform),Darwin)
+        LDLIBS += -L/usr/local/opt/readline/lib
+        INCLUDES += -I/usr/local/opt/readline/include
+    endif
+    LDLIBS += -lreadline
+    READLINE_FOUND = 1
 endif
-LDLIBS += -lreadline
 
 #######################################################################################################
 CFLAGS ?= $(DEFCFLAGS)
@@ -280,6 +283,10 @@ ifneq (,$(findstring MINGW,$(platform)))
     PM3CFLAGS += -mno-ms-bitfields -fexec-charset=cp850
 endif
 
+ifeq ($(READLINE_FOUND),1)
+    PM3CFLAGS += -DHAVE_READLINE
+endif
+
 ifeq ($(BT_FOUND),1)
     PM3CFLAGS += -DHAVE_BLUEZ
 endif
@@ -366,6 +373,16 @@ else
     endif
 endif
 
+ifeq ($(SKIPREADLINE),1)
+    $(info Readline library:  skipped)
+else
+    ifeq ($(READLINE_FOUND),1)
+        $(info Readline library:  enabled)
+    else
+        $(info Readline library:  Readline not found, disabled)
+    endif
+endif
+
 ifeq ($(SKIPWHEREAMISYSTEM),1)
     $(info Whereami library:  local library forced)
 else