InnoDB defines some functions that are not called at all. Other functions are called, but only from the same compilation unit.
Remove some function declarations and definitions, and add 'static' keywords. Some symbols must be kept for separately compiled tools, such as innochecksum.
Also, port the follow-up by Jon Olav Hauglid:
Bug#21153166: REMOVE UNUSED VARIABLES AND CONVERT GLOBAL SYMBOLS TO STATIC
Bug#21141390: REMOVE UNUSED FUNCTIONS AND CONVERT GLOBAL SYMBOLS TO STATIC
but for variables instead of functions.
Was identified with the -Wmissing-variable-declarations
compiler warning option supported by Clang 3.6.