Provide WITHOUT_BOTAN and WITHOUT_SYSTEMD cmake flags

Use them to build without linking to them, even if they are on your system

CMakeLists.txt

@@ -21,8 +21,12 @@ find_package(EXPAT REQUIRED)
 find_package(Iconv REQUIRED)
 find_package(Libuuid REQUIRED)
 find_package(Libidn)
-find_package(SystemdDaemon)
-find_package(Botan)
+if(NOT WITHOUT_SYSTEMD)
+  find_package(SystemdDaemon)
+endif()
+if(NOT WITHOUT_BOTAN)
+  find_package(Botan)
+endif()
 
 #
 ## Get the software version

INSTALL

@@ -78,10 +78,20 @@ using the POLLER cmake option.  Available values are:
  EPOLL: use the Linux-specific epoll(7). This is the default on Linux.
  POLL: use the standard poll(2). This is the default value on all non-Linux platforms.
 
-Example, configure the poller with cmake:
+Examples, configure the poller with cmake:
 
 % cmake . -DPOLLER=EPOLL
 
+You can also decide not to use two of the optional dependencies, even if they are present on your system, for example if Botan is available but you do not want to use it, you can set the value of WITHOUT_BOTAN to 1, like this:
+
+% cmake . -DWITHOUT_BOTAN=1
+
+This way, the binary will not be linked with libotan at all (and all
+connection will then be made in clear text).
+You can also decide not to link with systemd, like this:
+
+% cmake . -DWITHOUT_SYSTEMD=1
+
 
 ==============
     Build