[pcl] When cross-compiling pcl for Android pre-set some cache variables.

[jackjansen]

Fixes #41505.

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[jackjansen]

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[BillyONeal]

Can you explain what the effect of setting these is, and why it is correct to do so for Android?

[jackjansen]

Sorry for the delay in answering this.

The problem this fix solves is that these build-time tests depend on running a program to test the existence of some aligned-allocation functions. This cannot work when cross-compiling.

When building for Android you're always cross-compiling. Moreover, these macros aren't actually needed because they're used in one place in the pcl sources, and in that place there's a separate #if for Android.

I've reported the same issue in the pcl repo, but past experience suggests that the pcl developers move at glacial speed.

[jackjansen]

Superseded by #43295