x86: optimize %cr0 access

By removing redundant ands and ors with the compiler's kind assistance.
call L4_Lipc() from L4_Lcall(), L4_LreplyWait()

Previously they'd called plain old L4_Ipc(). That's wrong.

Also, update L4_Lipc() to clobber "memory", "cc" which it previously didn't,
but L4_Ipc() did.