auto merge of #16658 : jauhien/rust/fix-llvm, r=thestinger

Upstream LLVM from VCS already has version 3.6,
configure fixed appropriately to allow building with it

Author: bors

configure

@@ -635,7 +635,7 @@ then
     LLVM_VERSION=$($LLVM_CONFIG --version)
 
     case $LLVM_VERSION in
-        (3.[2-5]*)
+        (3.[2-6]*)
             msg "found ok version of LLVM: $LLVM_VERSION"
             ;;
         (*)