Add .arm directives for the GLX entrypoint stubs.

Add .arm and .thumb directives before and after the ARMv7 GLX dispatch stubs.

The function addresses that get passed around don't take Thumb into account, so
if they're compiled as Thumb, then they'd still get executed as ARM, which
would cause them to crash a SIGILL.
12 jobs for fix-glx-armv7-arm-directive in 1 minute and 53 seconds (queued for 1 second)