Don't suggest let bindings if they don't help with borrows

[PramodBisht]

@oli-obk I have added a condition to address #52049, right now, this is on WIP because I think code change is also required on error_reporting.rs. Plus I need to check if any test cases fail.
I will ping you again if everything passes

r? @oli-obk

[estebank]

@PramodBisht you'll need to create a new src/test/ui/suggestions file with the reproduction case and run ./x.py test src/test/ui --stage 1 --bless locally to create the appropriate .stderr file with the new output.

[rust-highfive]

The job x86_64-gnu-llvm-3.9 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

[00:41:53] .................................i..................................................................
[00:41:57] ......................i.............................................................................
[00:42:02] ....................................................................................................
[00:42:08] ....................................................................................................
aborting due to previous error\n\n"}
[00:42:17] thread 'main' panicked at 'Some tests failed', tools/compiletest/src/main.rs:498:22
[00:42:17] {"message":"For more information about this error, try `rustc --explain E0597`.","code":null,"level":"","spans":[],"children":[],"rendered":"For more information about this error, try `rustc --explain E0597`.\n"}
[00:42:17] ------------------------------------------
[00:42:17] 
[00:42:17] thread '[ui (nll)] ui/suggestions/issue-52059.rs' panicked at 'explicit panic', tools/compiletest/src/runtest.rs:3140:9
[00:42:17] note: Run with `RUST_BACKTRACE=1` for a backtrace.
---
[00:42:17] test result: FAILED. 1547 passed; 1 failed; 5 ignored; 0 measured; 0 filtered out
[00:42:17] 
[00:42:17] 
[00:42:17] 
[00:42:17] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/compiletest" "--compile-lib-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib" "--run-lib-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib" "--rustc-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "--src-base" "/checkout/src/test/ui" "--build-base" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui" "--stage-id" "stage2-x86_64-unknown-linux-gnu" "--mode" "ui" "--target" "x86_64-unknown-linux-gnu" "--host" "x86_64-unknown-linux-gnu" "--llvm-filecheck" "/usr/lib/llvm-3.9/bin/FileCheck" "--host-rustcflags" "-Crpath -O -Zunstable-options " "--target-rus

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:18010de0
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[PramodBisht]

all test passed.
cc @oli-obk @estebank

[oli-obk]

@bors r+

[bors]

📌 Commit ab767ee has been approved by oli-obk

[bors]

⌛ Testing commit ab767ee with merge 0e6b713...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: oli-obk
Pushing 0e6b713 to master...