install man pages for programs only if we're building those programs

CMakeLists.txt

@@ -173,10 +173,6 @@ install(
     FILES badvpn.7
     DESTINATION share/man/man7
 )
-install(
-    FILES badvpn-server.8 badvpn-client.8
-    DESTINATION share/man/man8
-)
 
 # reset variables indicating whether we're building various libraries,
 # and set them in the respective CMakeLists files. This is used to disable

client/CMakeLists.txt

@@ -23,3 +23,8 @@ install(
     TARGETS badvpn-client
     RUNTIME DESTINATION bin
 )
+
+install(
+    FILES badvpn-client.8
+    DESTINATION share/man/man8
+)

server/CMakeLists.txt

@@ -5,3 +5,8 @@ install(
     TARGETS badvpn-server
     RUNTIME DESTINATION bin
 )
+
+install(
+    FILES badvpn-server.8
+    DESTINATION share/man/man8
+)