Fixed buildver generated headers automake dependency tracking.

We now include buildver-sgen/boehm.h in BUILT_SOURCES to have proper dependency tracking for these generated files.

Fixes the MinGW OSX cross build.
Merge pull request #1339 from tritao/master

Fixed buildver generated headers automake dependency tracking.
Add missing header
Fix build on FreeBSD

pid_t (used at line 216) is available on Linux in `unistd.h` and so on on FreeBSD (`sys/types.h` to be precise, included in `unistd.h`), yet on FreeBSD this header is not automatically included.
Merge pull request #1340 from smortex/patch-1

Add missing header
Protect #include <unistd.h>

Protect inclusion as reported by @vargaz
Merge pull request #1341 from smortex/patch-2

Fix build on FreeBSD
Revert "Fixed buildver generated headers automake dependency tracking."

This reverts commit 8f41328a7811fee2798d95ed140e62b3198fc323.

Revert this for now as it breaks the parallel build.
[build] Rework the buildver dep check.
[jit] Fix the return of vtypes containing a single fp member from pinvoke methods on osx/x86. Fixes #23813.
Fixed linking on MinGW.
[io-layer] Make process handles non-shared. Fixes #23423.
[io-layer] Fix the linux build.
[corlib] Implement MonoGenericClass:GetCustomAttributes () for created types. Fixes #23769.
[io-layer] More coding convention/formatting fixes.
[runtime] Use getrlimit () to obtain the size of the fd table instead of getdtablesize () which is getting deprecated in Android.
[io-layer] Remove another usage of getdtablesize ().
Fix a warning.
[runtime] Add a 'shared_handles' --enable-minimal option, same as --disable-shared-handles.
Include ucontext.h on android if it exists.