Build System: Prevent unneeded changes to asterisk/buildopts.h.

* Add AST_DEVMODE to BUILDOPTS
* Remove CFLAGS that do not effect ABI from BUILDOPTS.
* Use BUILDOPTS to generate AST_BUILDOPT_SUM.
* Remove loop that defined AST_MODULE_*

These changes ensure that only ABI effecting options are considered for
AST_BUILDOPT_SUM.  This also reduces unneeded full system rebuilds caused
by enabling or disabling one module that another is dependent on.

ASTERISK-25028 #close
Reported by: Corey Farrell

Change-Id: I2c516d93df9f6aaa09ae079a8168c887a6ff93a2