Fix PAL_VirtualUnwind Behavior with Clutters in PC

Fix PAL_VirtualUnwind Behavior with Clutters in PC

Libunwind-ARM recommends to read LR to get value of PC
while unwinding stack, which often causes the caller
(PAL_VirtualUnwind) to have LSB of PC set.

Such behavior incurs errornous behavior of PAL_VirtualUnwind
if the output is fed back to PAL_VirtualUnwind as the input,
which is observed with VirtualUnwindToFirstManagedCallFrame().

This commit clears LSB of PC in WinContext to prevent it.

Note that this is a partial fix for the issue #3462.
(this does not fix assembly stacks)

Fix #3462

Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>