[Sanitizers][test] XFAIL long double tests on Solaris/sparc

As reported in Issue #41838, `clang` doesn't correctly implement `long
double` on 32-bit Solaris/SPARC: the psABI requires this to be an 128-bit
type.  Four sanitizer tests currently `FAIL` for this reason.

While there is a WIP patch to fix `clang` (D89130
<https://reviews.llvm.org/D89130>), it isn't complete yet and I've hit so
many brick walls while trying to finish it that I'm unsure if I ever will.

This patch therefore `XFAIL`s those tests in the meantime.

Tested on `sparcv9-sun-solaris2.11`.

Differential Revision: https://reviews.llvm.org/D119016