[mono] Add HAVE_PTHREAD_JIT_WRITE_PROTECT_NP to cmake config.h.in

[lambdageek]

Otherwise mono_codeman_enable_write is a no-op

Should fix jiting on macOS arm64

Fixes #49042

[lambdageek]

To test, on an M1:

$ arch -x86_64 ./build.sh mono+libs -c Debug --arch arm64
$ cd src/libraries/System.Buffers/tests
$ ../../../../dotnet.sh build /t:Test /p:TargetArchitecture=arm64

[lambdageek]

So interestingly, this seems to mean that JITing on arm64 in MacCatalyst apps is not possible. The pthread_jit_write_protect_np function is marked __API_AVAILABLE(macos(10.16)) __API_UNAVAILABLE(ios, tvos, watchos, bridgeos, driverkit) (pthread.h source here).

So this did not work:

$ arch -x86_64 ./build.sh mono+libs -c Debug --arch arm64 --os maccatalyst
$ cd src/libraries/System.Buffers/tests
$ ../../../../dotnet.sh build /t:Test /p:TargetArchitecture=arm64 /p:TargetOS=maccatalyst

I'm still investigating the crash to see if there's something else going wrong. But at first blush it seems like the write protection bit still needs to be toggled, but the API for doing so is not available.