Persist FPU variables across try_compile passes

[am11]

When -cmakeargs -DCLR_ARM_FPU_TYPE=vfpv4 is passed from command-line, the first pass to toolchain was failing the condition if (NOT DEFINED CLR_ARM_FPU_TYPE) as expected, but the second and subsequent passes were satisfying the condition. This is because how cmake invokes the toolchain file.

Append variables the must persist across the passes to CMAKE_TRY_COMPILE_PLATFORM_VARIABLES to override this behavior.

Second issue was that we weren't propagating cmakeargs in corehost.proj and build-native.proj properly; missing -cmakeargs argument name. Note that src/coreclr/runtime.proj already handles it.

Fixes #83170.
Upstream PR dotnet/arcade#12817

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Issue Details

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When -cmakeargs -DCLR_ARM_FPU_TYPE=vfpv4 is passed from command-line, the first pass to toolchain was failing the condition if (NOT DEFINED CLR_ARM_FPU_TYPE) as expected, but the second and subsequent passes were satisfying the condition. This is because how cmake invokes the toolchain file.

Append variables we must persist across the passes to CMAKE_TRY_COMPILE_PLATFORM_VARIABLES to override this behavior.

Second issue was that we weren't propagating cmakeargs in corehost.proj and build-native.proj properly; missing -cmakeargs argument name.

Fixes #83170.
Upstream PR #12817

Author:	am11
Assignees:	-
Labels:	area-Infrastructure-libraries
Milestone:	-

[ghost]

Tagging subscribers to this area: @dotnet/runtime-infrastructure
See info in area-owners.md if you want to be subscribed.

Issue Details

---

When -cmakeargs -DCLR_ARM_FPU_TYPE=vfpv4 is passed from command-line, the first pass to toolchain was failing the condition if (NOT DEFINED CLR_ARM_FPU_TYPE) as expected, but the second and subsequent passes were satisfying the condition. This is because how cmake invokes the toolchain file.

Append variables we must persist across the passes to CMAKE_TRY_COMPILE_PLATFORM_VARIABLES to override this behavior.

Second issue was that we weren't propagating cmakeargs in corehost.proj and build-native.proj properly; missing -cmakeargs argument name.

Fixes #83170.
Upstream PR #12817

Author:	am11
Assignees:	-
Labels:	area-Infrastructure
Milestone:	-

[am11]

@janvorli PTAL. Trying to avoid merge conflicts with other PRs changing these lines. :)

[janvorli]

LGTM, thank you! I have thought that I have already approved this, but obviously I was daydreaming.

[am11]

Mono failures are unrelated, wasm-windows: #64227, ios: #82083.