Bump to mono:2018-02

Commit list for mono/mono:

* mono/mono@279d7e230fd [2018-02] [threads] Fix race between abort socket syscall and thread shutdown (#7521)
* mono/mono@2ce1d5f3d51 Comment/stub out some unused icalls to prevent problems with AOT.
* mono/mono@668baf19156 [acceptance-tests] Actually disable gcsuppressfinalize.exe test
* mono/mono@2201952d9a7 WebRequestStream now throws correct exception on cancellation (#7074).
* mono/mono@4d3e9d53b25 Fix resolution of interfaces in classes implementing IEnumerator. Fixes #59400
* mono/mono@2476d2ac060 Move the check for open constructed types later in mono_jit_compile_method_with_opt (), this function can receive gshared methods in llvmonly mode. (#7504)
* mono/mono@91fe1eb5f58 Fix generated file when passing --bundled-header (#7510)
* mono/mono@bb0c123e74d Use runtime template for iOS
* mono/mono@e965e1647d0 Use runtime template for Android
* mono/mono@a6522973840 Create common runtime compilation template
* mono/mono@685d39238a4 Have RELEASE be empty when CONFIGURATION != 'release'
* mono/mono@3648ace2b9d Move common targets
* mono/mono@b62bfdcb554 An array is not an IEnumerator`1
* mono/mono@9f2841c3a00 An array is not an IEnumerator`1
* mono/mono@6f90188e9fe Add IEnumerator`1 to MonoDefaults struct
* mono/mono@84027bddaaf Remove compiler config sections for types which cannot be instantiated
* mono/mono@66f19a974ad Swap Close/Dispose calls so that the receiver_thread_main loop will be properly interrupted
* mono/mono@99b7f59ddc1 [2018-02] Fix for gcc 4.4; nominal support for older. (#7435)
* mono/mono@f28abdbebd4 Fixes decoding of CMS/PKCS #7 messages with an explicit cryptographic object identifier
* mono/mono@2dc56b5a602 [2018-02] [corlib] Ignore TimeZoneTest.TestCtors on iOS under certain conditions due to an Apple bug. (#7428)
* mono/mono@58d02a96038 [acceptance-tests] Disable gcsuppressfinalize.exe test that started failing

Diff: mono/mono@fa1ec4a...279d7e2

https://bugzilla.xamarin.com/show_bug.cgi?id=59400