Clang: partman_devices.c is not, in fact, C++ code

CMakeLists.txt

@@ -29,7 +29,7 @@
 #
 #   cmake . -DSKIP_MODULES="partition luksbootkeycfg"
 
-project( calamares CXX )
+project( calamares C CXX )
 
 cmake_minimum_required( VERSION 3.2 )
 

src/modules/welcome/CMakeLists.txt

@@ -5,8 +5,6 @@ find_package( Qt5 ${QT_VERSION} CONFIG REQUIRED DBus Network )
 
 include_directories( ${PROJECT_BINARY_DIR}/src/libcalamaresui )
 
-set_source_files_properties( checker/partman_devices.c PROPERTIES LANGUAGE CXX )
-
 set( CHECKER_SOURCES
     checker/CheckItemWidget.cpp
     checker/CheckerWidget.cpp

src/modules/welcome/checker/partman_devices.h

@@ -19,6 +19,14 @@
 #ifndef PARTMAN_DEVICES_H
 #define PARTMAN_DEVICES_H
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 int check_big_enough(long long required_space);
 
+#ifdef __cplusplus
+}  // extern "C"
+#endif
+
 #endif // PARTMAN_DEVICES_H