ART: Rewrite stub-test inline assembly

Rewrite the x86 and x86-64 inline assembly to spill and restore
registers manually. GCC outright rejected clobbering some registers,
but Clang silently ignored the problematic cases, which breaks,
for example, in ASAN builds.

Bug: 24294564
Change-Id: Iab45da0d6082ad77435e75bdc41d547619443d47