cmake: set Qt 5.12 as minimum

CMakeLists.txt

@@ -150,6 +150,8 @@ if(UNIX)
   endif()
 endif()
 
+set(QT_MIN_VERSION "5.12")
+
 find_package(PkgConfig REQUIRED)
 
 # TODO: drop this once we switch to Qt 5.14+
@@ -165,7 +167,7 @@ if(Qt5XmlPatterns_FOUND)
 endif()
 
 foreach(QT5_MODULE ${QT5_LIBRARIES})
-  find_package(${QT5_MODULE} REQUIRED)
+  find_package(${QT5_MODULE} ${QT_MIN_VERSION} REQUIRED)
   include_directories(${${QT5_MODULE}_INCLUDE_DIRS})
 endforeach()
 

README.md

@@ -94,7 +94,7 @@ Packaging for your favorite distribution would be a welcome contribution!
 
 ## Compiling the Monero GUI from source
 
-*Note*: Qt 5.9.7 is the minimum version required to build the GUI.
+*Note*: Qt 5.12 is the minimum version required to build the GUI.
 
 *Note*: Official GUI releases use monero-wallet-gui from this process alongside the supporting binaries (monerod, etc) from the [CLI deterministic builds](https://github.com/monero-project/monero/blob/release-v0.18/contrib/gitian/README.md).