Bump mono. (#4971)

Commit list for mono/mono:

* mono/mono@2343f267067 [sdks] Add cmake toolchain file for LLVM MXE builds (#11056)
* mono/mono@46b723d6b01 [2018-06] [sdks] Create archive targets for pre-building on CI (#10936)
* mono/mono@ab3c897d685 Merge pull request #10997 from lewurm/2018-06-interp-fixes-for-native-type
* mono/mono@914a62ab2e7 [interp] introduce float R4 stack type
* mono/mono@62f23a83652 [interp] support ntype.ToString ()
* mono/mono@2c48c62e66f [interp] support nfloat.*Infinity
* mono/mono@5c5a48b1449 [interp] support ntype.Equals ()
* mono/mono@13e412ee52a [interp] support ntype.CompareTo ()
* mono/mono@a576a799b16 [interp] fix op_implicit/op_explicit conversions for native types
* mono/mono@1d9378713e6 [sdks/ios] Build libMonoPosixHelper for device architectures, so that zlib-helper.o is created. (#10921) (#10970)
* mono/mono@6e48ad4f7b1 Merge pull request #10905 from monojenkins/backport-pr-10899-to-2018-06
* mono/mono@d050e323ed9 [runtime] Fix undefined pthread_main_np (#10930)
* mono/mono@b549fa7f32a [Reflection] Fix issue with finding types in module using an asterisk as filter criteria
* mono/mono@0dffbef2690 Bump corefx to disable more tests
* mono/mono@6c46acfe697 [runtime] Disable stack guard for main thread on osx
* mono/mono@46e0249d4cd [sdks] One more update to get XA PR builds working on Linux (#10855)
* mono/mono@910395a05f6 corefx bump
* mono/mono@2cdfb380a3e [2018-06] [System]: Make sure `HttpWebRequest` observes exceptions on timeout.  #10488. (#10732)
* mono/mono@aebef84fa2c [merp] Fix return value handling of posix_spawn (#10828)
* mono/mono@59f2dbf28b0 [sdks] Debian Linux doesn't need to build MXE (#10819)
* mono/mono@401bce867d3 Bump msbuild to track mono-2018-06
* mono/mono@65737564b04 Bump corefx
* mono/mono@40d991c3257 [SDKS] Build host runtime with correct bitness (#10742)
* mono/mono@1a71d5101f2 [crash] Fix summarize_frame assertion
* mono/mono@8f36212ad3a [2018-06] Ignore some xunit tests for XA (non compatible with xunit 2.4) (#10721)
* mono/mono@410792459a8 [corlib] Makes remoting test more robust (and disable it on mobile)
* mono/mono@7dd65f79a53 [mono-api-html] Render something for fields with marshalling info. (#10698)
* mono/mono@7c898271e73 [offset-tool] Error out when parsing fails. (#10696)
* mono/mono@adbb8f72c8b [2018-06] Implement IEnumerable for ConditionalWeakTable (#10657)

Diff: mono/mono@1b18f39...2343f26