Only require Qt5 when building the GUI

Commit 6c888437 made Qt5 mandatory for all builds when it is only
required for the GUI. There's already a find_package call in src/gui,
it just needed the REQUIRED flag to be added.

CMakeLists.txt

@@ -357,12 +357,6 @@ else()
     set (OPENSSL_LIBS ${lib_ssl} ${lib_crypto})
 endif()
 
-
-# Check we have the *required* Qt5 libs.
-find_package(Qt5Core REQUIRED)
-find_package(Qt5Network REQUIRED)
-find_package(Qt5Widgets REQUIRED)
-
 #
 # Configure_file... but for directories, recursively.
 #

src/gui/CMakeLists.txt

@@ -1,6 +1,6 @@
 cmake_minimum_required (VERSION 3.4)
 
-find_package (Qt5 COMPONENTS Core Widgets Network)
+find_package (Qt5 REQUIRED COMPONENTS Core Widgets Network)
 set (CMAKE_AUTOMOC ON)
 set (CMAKE_AUTORCC ON)
 set (CMAKE_AUTOUIC ON)