[libc++] Run picolibc tests with qemu

This patch actually runs the tests for picolibc behind an emulator,
removing a few workarounds and increasing coverage.

Differential Revision: https://reviews.llvm.org/D155521

GitOrigin-RevId: be811d1617654e46f4f4daa82259ae4fad4c8e6a
1 file changed