[qfcc] Allow aligned despace allocs to be overridden

GLSL (and in the end, spir-v) needs more control over allocation than
does the Ruamoko VM.

tools/qfcc/include/defspace.h

@@ -60,6 +60,19 @@ typedef struct defspace_s {
 	int         size;			///< current high-water mark for alloced data
 	int         max_size;		///< size of backing memory, or highwater mark
 								///< for ds_virtual
+	/** Optional callback for aligned allocation of space
+
+		Overrides defspace_alloc_aligned_loc.
+
+		\param space	This defspace.
+		\param size     Size of space to allocate. Must be > 0.
+		\param alignment Requested alignment for the space. Must be > 0.
+		\return         The offset of the allocated space. If allocation fails
+						(because the backing memory cannot be grown), it is
+						treated as an internal error.
+	*/
+	int       (*alloc_aligned) (struct defspace_s *space, int size,
+								int alignment);
 	/** Grow the backing memory of the defspace.
 
 		This function is called when more memory is needed for the space.

tools/qfcc/source/defspace.c

@@ -159,6 +159,9 @@ defspace_alloc_loc (defspace_t *space, int size)
 int
 defspace_alloc_aligned_loc (defspace_t *space, int size, int alignment)
 {
+	if (space->alloc_aligned) {
+		return space->alloc_aligned (space, size, alignment);
+	}
 	int         ofs, pad;
 	locref_t   *loc;
 	locref_t  **l = &space->free_locs;