Prevent CMake from using -isystem instead of -I for include directories of...

Prevent CMake from using -isystem instead of -I for include directories of targets imported by find_package().

cmake/CMakeLists.txt

@@ -98,6 +98,7 @@ list(APPEND LINPHONE_BUILDER_EP_VARS
 	CMAKE_MODULE_LINKER_FLAGS:STRING
 	CMAKE_MODULE_PATH:PATH
 	CMAKE_NO_BUILD_TYPE:BOOL
+	CMAKE_NO_SYSTEM_FROM_IMPORTED:BOOL
 	CMAKE_PREFIX_PATH:STRING
 	CMAKE_PROGRAM_PATH:STRING
 	CMAKE_RUNTIME_OUTPUT_DIRECTORY:PATH

prepare.py

@@ -65,6 +65,7 @@ class Target:
             cmd += ['-A', self.platform_name]
         cmd += ['-DCMAKE_BUILD_TYPE=' + build_type]
         cmd += ['-DCMAKE_PREFIX_PATH=' + self.output_dir(), '-DCMAKE_INSTALL_PREFIX=' + self.output_dir()]
+        cmd += ['-DCMAKE_NO_SYSTEM_FROM_IMPORTED=YES']
         cmd += ['-DLINPHONE_BUILDER_WORK_DIR=' + self.abs_work_dir]
         if self.toolchain_file is not None:
             cmd += ['-DCMAKE_TOOLCHAIN_FILE=' + self.toolchain_file]