Use warnings.el:

Use warnings.el:
(byte-compile-warning-prefix): New function.
(byte-compile-log-file): Return page start position.
(byte-compile-log-warning): New function.
(byte-compile-warn): Use byte-compile-log-warning.
(byte-compile-report-error): Likewise.  Also use error-message-string.
(displaying-byte-compile-warnings): Bind warning-series.
Don't bind or use byte-compile-warnings-point-max.
Don't display the log buffer at the end.
(byte-compile-warnings-point-max): Variable deleted.
(byte-compile-log-1): Rewrite for trace info, not used for warnings.
(byte-compile-last-warned-form, byte-compile-last-logged-file):
Defvars moved.