Bump to latest mono 2018-02 @4fe3280 (#4487)

Commit list for mono/mono:

* mono/mono@4fe3280bba1 Revert "[sdk] Do not fix android platform-tools version. Make it configurable. (#9508)"
* mono/mono@12ae4f9b0c6 Revert "[runtime] Fix the --enable-minimal=aot build. (#9394)"
* mono/mono@a2b95fbb4b2 Revert "[2018-02] Backport /bin/bash shell set for wasm"
* mono/mono@f795aa5d2db [llvm] Avoid using the preserveall calling convention in another place on watchos. (#9578)
* mono/mono@04493d22247 Fix LogcatTextWriter_Log interpreting messages it logs, potentially writing random garbage and/or crashing (introduced by mono/mono@984f648) (Fixes dotnet/android#1951) (#9612)
* mono/mono@35284c340c0 [runtime] Make sigterm dumper send file to merp (#9586)
* mono/mono@077307fce4b [sdk] Do not fix android platform-tools version. Make it configurable. (#9508)
* mono/mono@1ad118647cd [arm64] Make OP_CHECK_THIS read only a byte, to prevent unaligned access errors. (#9546)
* mono/mono@86f99d31bd3 Merge pull request #9483 from alexanderkyte/2018-02-merp_params
* mono/mono@97aa066389e [2018-02] Backport /bin/bash shell set for wasm
* mono/mono@37091f00c29 [runtime] Enable application to register path for MERP restart
* mono/mono@955ad4538ec [runtime] Make merp eventType icall argument
* mono/mono@fc0c12f768b [Coop] Convert Mono.Runtime to coop. (#8599)
* mono/mono@c495285cac4 [debugger] more locking and avoid race around mono_threads_join_lock & loader lock
* mono/mono@d18b8941ab7 [debugger] Add locking around tls->frames usage/freeing
* mono/mono@1bdbf71a8b2 [runtime] Fix the --enable-minimal=aot build. (#9394)

Diff: mono/mono@cae8c54...4fe3280