Darwin: Adjust the PCH area to allow for 16384byte page size.

Newer versions of Darwin report pagesize 20 which means that we
need to adjust the aligment of the PCH area.

gcc/ChangeLog:

	* config/host-darwin.c: Align pch_address_space to 16384.

Author: iains

gcc/config/host-darwin.c

@@ -24,7 +24,10 @@
 #include "config/host-darwin.h"
 
 /* Yes, this is really supposed to work.  */
-static char pch_address_space[1024*1024*1024] __attribute__((aligned (4096)));
+/* This allows for a pagesize of 16384, which we have on Darwin20, but should
+   continue to work OK for pagesize 4096 which we have on earlier versions.
+   The size is 1 (binary) Gb.  */
+static char pch_address_space[65536*16384] __attribute__((aligned (16384)));
 
 /* Return the address of the PCH address space, if the PCH will fit in it.  */