how to use lmem.h ?

[Bertrand Mansion <lua@...>]

I am trying to create a C module for Lua. One of the functions deals
with string quoting so I need to allocate a buffer with 2 times +1 the
memory occupied by the source string. Usually, I would use malloc()
but I noticed that there is a lmem.h file with a luaM_malloc()
function, so I could write something like this:
  to = luaM_malloc(L, 2 * size);

Unfortunately, #include "lmem.h" doesn't work if I install Lua using
the default Makefile (I am on Macosx). Is there a way to build Lua or
some extra steps I should do manually in order to be able to use
"lmem.h" ? Thanks,

-- 
Bertrand Mansion
Mamasam