Changing any Menuselect option in the `Compiler Flags` section causes a
full rebuild of the Asterisk source tree.  Every enabled option causes
a #define to be added to buildopts.h, thus breaking ccache caching for
every source file that includes "asterisk.h".  In most cases each option
only applies to one or two files.  Now we only define those options for
the specific sources which use them, this causes much better cache
matching when working with multiple builds.  For example testing code
with an without MALLOC_DEBUG will now use just over half the ccache
size, only main/astmm.o will have two builds cached instead of every
file.

Reorder main/Makefile so _ASTCFLAGS set on specific object files are all
together, sorted by filename.  Stop adding -DMALLOC_DEBUG to CFLAGS of
bundled pjproject, this define is no longer used by any header so only
serves to break cache.

The only code change is a slight adjustment to how main/astmm.c is
initialized.  Initialization functions always exist so main/asterisk.c
can call them unconditionally.  Additionally rename the astmm
initialization functions so they are not exported.

Change-Id: Ie2085237a964f6e1e6fff55ed046e2afff83c027