Auto merge of #870 - micbou:no-7zip-prompt, r=bstaletic

[READY] Run 7-Zip in non-interactive mode

When doing an incremental build on Windows, CMake will be stuck extracting libclang from the installer because 7-Zip asks the user if he want to overwrite existing files. We can avoid that by adding the `-y` option to the 7-Zip command.

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cpp/ycm/CMakeLists.txt

@@ -122,7 +122,8 @@ if ( USE_CLANG_COMPLETER AND
         "7-zip is needed to extract the files from the Clang installer. "
         "Install it and try again." )
     endif()
-    execute_process( COMMAND ${7Z_EXECUTABLE} x ${CLANG_FILENAME} OUTPUT_QUIET )
+    execute_process( COMMAND
+                     ${7Z_EXECUTABLE} -y x ${CLANG_FILENAME} OUTPUT_QUIET )
   else()
     execute_process( COMMAND tar -xzf ${CLANG_FILENAME} )
   endif()