[lldb/test] Fix arch arm for 32-bit armv7l/armv8l

This patch forces architecture "arm" if underlying os reports core
armv7l or armv8l. On linux systems 32 bit sysroot running on 64bit
AArch64 hardware reports armv7l or armv8l which is essently arm
32bit mode. This fixes 5 testcases on 32bit arm.