fix: Clean repo builds no longer fail when building native

[bitsandfoxes]

When building the SDK I keep having the build break on me with.

Sentry net8.0 failed with 2 error(s) (3.2s)
  EXEC : CMake error : CMAKE_CXX_COMPILER not set, after EnableLanguage
  /Users/bitfox/Workspace/sentry-unity/src/sentry-dotnet/src/Sentry/Platforms/Native/Sentry.Native.targets(93,5): error MSB3073: The command "pwsh ../../scripts/build-sentry-native.ps1 -Clean" exited with code 1.
Sentry net9.0 failed with 1 error(s) (3.0s)
  /Users/bitfox/Workspace/sentry-unity/src/sentry-dotnet/src/Sentry/Platforms/Native/Sentry.Native.targets(93,5): error MSB3073: The command "pwsh ../../scripts/build-sentry-native.ps1 -Clean" exited with code 1.

Digging through it I run into this

Sentry net9.0 failed with 1 error(s) (6.1s)
      -- The C compiler identification is AppleClang 17.0.0.17000013
      -- ... a bunch of other flags ...
      -- Build files have been written to: /Users/bitfox/Workspace/sentry-unity/src/sentry-dotnet/modules/sentry-native/build
      [  0%] Building C object CMakeFiles/sentry.dir/vendor/mpack.c.o
      [100%] Linking C static library libsentry.a
      [100%] Built target sentry
      Copying modules/sentry-native/build/libsentry.a to src/Sentry/Platforms/Native/sentry-native/osx/libsentry-native.a
      Copy-Item: /Users/bitfox/Workspace/sentry-unity/src/sentry-dotnet/scripts/build-sentry-native.ps1:88
      Line |
        88 |      Copy-Item -Force -Path $srcFile -Destination $outFile
           |      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           | Cannot find path
           | '/Users/bitfox/Workspace/sentry-unity/src/sentry-dotnet/modules/sentry-native/build/libsentry.a' because it does not exist.
      /Users/bitfox/Workspace/sentry-unity/src/sentry-dotnet/src/Sentry/Platforms/Native/Sentry.Native.targets(93,5): error MSB3073: The command "pwsh /Users/bitfox/Workspace/sentry-unity/src/sentry-dotnet/scripts/build-sentry-native.ps1 -Clean" exited with code 1.
    Sentry net8.0 succeeded (6.7s) → src/Sentry/bin/Debug/net8.0/Sentry.dll
      -- The C compiler identification is AppleClang 17.0.0.17000013
      -- ... a bunch of other flags ...
      -- Build files have been written to: /Users/bitfox/Workspace/sentry-unity/src/sentry-dotnet/modules/sentry-native/build
      [ 23%] Building C object CMakeFiles/sentry.dir/vendor/mpack.c.o
      [ 96%] Building C object CMakeFiles/sentry.dir/src/transports/sentry_transport_none.c.o
      Linking C static library libsentry.a
      Built target sentry
      Copying modules/sentry-native/build/libsentry.a to src/Sentry/Platforms/Native/sentry-native/osx/libsentry-native.a

looks like building Sentry causes the build native target to run in parallel, corrupting the build output and failing.

So instead, we make use of this article explaining how to run a target really only once.

While debugging, the resolving the path to the build script kept breaking. So instead of ../.. we can go with $(MSBuildThisFileDirectory)_and then relative path from here_.

#skip-changelog

[bitsandfoxes]

We have to keep the condition on the "outer" target as the TF gets removed on line 108

[bitsandfoxes]

The "when" now gets resolved by this target being "clamped" by the two new ones.

[bitsandfoxes]

The condition needs to be added to the new one's as '$(_SentryIsNet8OrGreater)' == 'true' does not resolve due to TF being removed.

[vaind]

I'm flabbergasted how the target change helps at all... but if it does... 🤷

[Flash0ver]

Thanks for making our build a bit better.

I can imagine something similar will help me with #4307.
More pre-processed MSBuild project files for me to read,
and more .binlogs to explore get lost in, especially now with #4358.