Let the buffer just use the default size by specifying 0 as the size

instead of specifying the default size explicitely.

Submitted by:	Max Okumoto <okumoto@ucsd.edu>

usr.bin/make/var.c

@@ -1751,7 +1751,7 @@ Var_Subst(const char *var, char *str, GNode *ctxt, Boolean undefErr)
 					 * been reported to prevent a plethora
 					 * of messages when recursing */
 
-    buf = Buf_Init(MAKE_BSIZE);
+    buf = Buf_Init(0);
     errorReported = FALSE;
 
     while (*str) {