RESTRICT AUTOMERGE: Add symlink for mediacodec-x86_64.policy

When building for x86 *without* TARGET_2ND_ARCH set, the build fails
because the mediacodec-$(TARGET_ARCH).policy expands to
mediacodec-x86_64.policy, which doesn't exist. Create it.

Bug: 158658685
Change-Id: I11108a62fac6fc9dcf47c0acd908663e155252cd
1 file changed