Bump corefx for credscan fixes (mono#21018)

Bump to mono/corefx@38e9a93

Diff: mono/corefx@7c24bb0...38e9a93

Primarily CredScan fixes.

Bump before we do a backport to 2020-02 of mono#21016 which will need one more corefx bump

[arm64] Fix wrong marshalling in gsharedvt transition (mono#21006)

Transitioning from ArgVtypeByRefOnStack to ArgVtypeByRef requires no marshalling. The reference ends up being saved on stack the same way and the stack slot just needs to be copied (in mono_arm_start_gsharedvt_call).

Bump fsharp.py to get upstream nuget feed cleanup

myget.org feeds were disabled recently.

(cherry picked from commit dbc5d75)

[2020-02] Bump msbuild, roslyn and nuget (mono#20983)

Bump to MSBuild vs16.9, Roslyn 3.9.0 and NuGet 5.9.0

Backport of mono#20979

Fix the System.String.Replace throwing NotImplementedException (mono#…

…20960) (mono#20978)

mono#20948

Build iOS SDK archives on Xcode 12.4

[2020-02][marshal] Fix VARIANT and BSTR marshaling in structs (mono#2…

…0918)

* [tests] Add BStr and VARIANT in structs interop tests

* [marshal] Fix reverse P/Invoke marshaling VARIANT fields

Partial revert of mono#8732

If a managed struct is declared as

        public struct StructWithVariant
        {
            [MarshalAs (UnmanagedType.Struct)]
            public object data;
        };

Then the `data` field should be marshalled as a VARIANT.

The fix checks that the field's type is `object` and uses VARIANT for
marshaling, otherwise it continues as in mono#8732 and uses
MONO_MARSHAL_CONV_OBJECT_STRUCT

* [marshal] Marshal BSTR from reverse pinvokes

Don't include mono-dtrace.h when generating offsets

offsets-tool can run before mono-dtrace.h is generated which leads to a compiler error about the file missing.

Disable DebuggerTests.Crash since it fails on Linux i386 in CI

See mono#20905

(cherry picked from commit 7eb6305)

Bump bockbuild to include mono/bockbuild#168