mpg123: updated to 1.32.4

1.32.4

build:
Reorganize shared headers, API headers into src/include.
Use relative include paths, avoiding internal directories in CPPFLAGS except for config.h.
Group C99 feature checks and make several standard headers mandatory.
Get rid of SIZE_P, OFF_P and friends.
Only enforce dummy module together with libout123, to be able to build individual modules using --disable-components logic.

out123:
added --libversion

libmpg123:
Avoid indirect branches into the assembly routines by using C wrappers also for dct36, relieving us of the need to care for bti / endbr instructions for control flow integrity.

(adam)