Auto merge of #912 - qhsong:master, r=micbou

Download libclang and llvm from https

Change libclangsource to https to avoid some http hijack.

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cpp/ycm/CMakeLists.txt

@@ -116,7 +116,7 @@ if ( USE_CLANG_COMPLETER AND
     set( CLANG_PACKAGE "libclang" )
   else()
     set( CLANG_URL
-         "http://releases.llvm.org/${CLANG_VERSION}/${CLANG_FILENAME}" )
+         "https://releases.llvm.org/${CLANG_VERSION}/${CLANG_FILENAME}" )
     set( CLANG_PACKAGE "Clang" )
   endif()