[asan][test] Fix `TestCases/alloca_*` ptr-to-long cast on Windows

[asan][test] Fix `TestCases/alloca_*` ptr-to-long cast on Windows

64-bit Windows uses 32-bit long so these casts fail to compile with the
error "cast from pointer to smaller type". Change to instead use
uintptr_t like other tests.

Differential Revision: https://reviews.llvm.org/D147232