[jit] Avoid extending the size of Vector2/Vector3 to 16 bytes. Disable SIMD for these types for now, since the SIMD code can't handle types (#6746)

which are smaller than a SIMD reg.

Fixes https://github.com/mono/mono/issues/6411.

Previously, 5174f7ed was an attempt to
correct this issue. However, the `#define` scheme for Mono changed since
then, so `PLATFORM_MACOSX` became `HOST_DARWIN`.

This change uses the proper define to correct Unity case 1166108.

[sdb] Avoid stack overflows caused by recursive calls between suspend_current () and invoke_method (). (#13362)

Fixes https://github.com/mono/mono/issues/13261.

On macOS and FAT32 partitions, we will sometimes get this inode value
for more than one file. It means the file is empty.  When this happens,
the hash table of file shares becomes corrupt, since more then one file
has the same inode. Instead, let's assume it is always fine to share
empty files. (Unity case 950616).

Fix crash during async debugging (case 1153078). Apply partial patch from https://github.com/mono/mono/commit/284c5afdf4363aec956ce370c86fc44458fffe6c

Fix liveness recursion issue (case 1137077). Cherry-pick of https://github.com/Unity-Technologies/mono/commit/0fb8f1f8bf17e6d51059a263680eb87025079028

This change builds the class library code to implement the
`NamedPipeClientStream` class in the unityaot profile on Windows. For
the time being, we will not implement this class for non-Windows
platforms, since that requires the Mono.Posix.dll assembly and a native
library as well.

We may consider adding support on Posix platforms in the future.

[Backport 2018.4-mbe] Stevedore+Gitlab+Yamato changes