C code bug fixes

- fix to buildin.c to prevent compiler from optimizing it out
- fix to realpath.c to handle case where 'path' is NULL

- fix to emacs.c (I think from dgk)

- fix to file.c (I think from gsf)
- fix to tail.c (I think from gsf)

- fix to code setting the malloc init hook (for vmalloc)

- changed memcpy to memmove in several places in sfio because src and dst
  might overlap

- fixes to macros like FILE_defined to fix header file issues
- fixes to expr.h to handle macro definition issue

src/lib/libast/sfio/sfflsbuf.c

@@ -96,7 +96,7 @@ int	c;	/* if c>=0, c is also written out */
 		isall = SFISALL(f,isall);
 		if((w = SFWR(f,data,n,f->disc)) > 0)
 		{	if((n -= w) > 0) /* save unwritten data, then resume */
-				memcpy((char*)f->data,(char*)data+w,n);
+				memmove((char*)f->data,(char*)data+w,n);
 			written += w;
 			f->next = f->data+n;
 			if(c < 0 && (!isall || n == 0))

src/lib/libast/sfio/sfmove.c

@@ -190,7 +190,7 @@ reg int		rc;	/* record separator */
 		{	/* move left-over to read stream */
 			if(w > fr->size)
 				w = fr->size;
-			memcpy((Void_t*)fr->data,(Void_t*)cp,w);
+			memmove((Void_t*)fr->data,(Void_t*)cp,w);
 			fr->endb = fr->data+w;
 			if((w = endb - (cp+w)) > 0)
 				(void)SFSK(fr,(Sfoff_t)(-w),SEEK_CUR,fr->disc);
@@ -200,7 +200,7 @@ reg int		rc;	/* record separator */
 		{	if(direct == SF_WRITE)
 				fw->next += r;
 			else if(r <= (fw->endb-fw->next) )
-			{	memcpy((Void_t*)fw->next,(Void_t*)next,r);
+			{	memmove((Void_t*)fw->next,(Void_t*)next,r);
 				fw->next += r;
 			}
 			else if((w = SFWRITE(fw,(Void_t*)next,r)) != r)

src/lib/libast/sfio/sfpool.c

@@ -138,7 +138,7 @@ int		n;	/* current position in pool	*/
 			else	/* write failed, recover buffer then quit */
 			{	if(w > 0)
 				{	v -= w;
-					memcpy(head->data,(head->data+w),v);
+					memmove(head->data,(head->data+w),v);
 				}
 				head->next = head->data+v;
 				goto done;
@@ -147,7 +147,7 @@ int		n;	/* current position in pool	*/
 
 		/* move data from head to f */
 		if((head->data+k) != f->data )
-			memcpy(f->data,(head->data+k),v);
+			memmove(f->data,(head->data+k),v);
 		f->next = f->data+v;
 	}
 

src/lib/libast/sfio/sfrd.c

@@ -201,7 +201,7 @@ Sfdisc_t*	disc;
 				if(buf)
 				{	if(n > (size_t)(r-a))
 						n = (ssize_t)(r-a);
-					memcpy(buf,f->next,n);
+					memmove(buf,f->next,n);
 					f->next += n;
 				}
 				else	n = f->endb - f->next;

src/lib/libast/sfio/sfread.c

@@ -92,7 +92,7 @@ size_t		n;	/* number of bytes to be read. 	*/
 		{	if(r > (ssize_t)n)
 				r = (ssize_t)n;
 			if(s != f->next)
-				memcpy(s, f->next, r);
+				memmove(s, f->next, r);
 			f->next += r;
 			s += r;
 			n -= r;

src/lib/libast/sfio/sfvscanf.c

@@ -247,7 +247,7 @@ Void_t*		mbs;	/* multibyte parsing state	*/
 	/* shift left data so that there will be more room to back up on error.
 	   this won't help streams with small buffers - c'est la vie! */
 	if(sc->d > sc->f->data && (n = sc->endd - sc->d) > 0 && n < SFMBMAX)
-	{	memcpy(sc->f->data, sc->d, n);
+	{	memmove(sc->f->data, sc->d, n);
 		if(sc->f->endr == sc->f->endb)
 			sc->f->endr = sc->f->data+n;
 		if(sc->f->endw == sc->f->endb)