Byte compiler: fix spurious warnings "might not be defined at runtime".

Byte compiler: fix spurious warnings "might not be defined at runtime".

Also initialize byte-compile-noruntime-functions between runs.

bytecomp.el (byte-compile-new-defuns): New variable.
(byte-compile-initial-macro-environment): For eval-when-compile: bind
byte-compile-unresolved-functions and byte-compile-new-defuns around
byte-compile-top-level, to prevent spurious entries being made.
(byte-compile-warn-about-unresolved-functions): Check whether function is in
byte-compile-new-defuns before emitting a warning about it.
(byte-compile-from-buffer): Initialize new variable and
byte-compile-noruntime-functions to nil.
(byte-compile-file-form-require): record all new functions defined by a
`require' in byte-compile-new-defuns.
(byte-compile-file-form-defmumble): record the new alias in
byte-compile-new-defuns.