Move _cygheap_start into .cygheap section.

Binutils >= 2.41 started making .rsrc section read-only, which caused
memset(_cygheap_start, ...) to segfault.  Instead, put _cygheap_start in
the .cygheap section, which makes more sense anyway, but may result in
reducing the difference between _cygheap_start and _cygheap_end by the
fraction of a page not used in the .rsrc section.

Fixes msys2#200
See-also: https://cygwin.com/pipermail/cygwin/2024-February/255472.html
Signed-off-by: Jeremy Drake <github@jdrake.com>

winsup/cygwin/cygwin.sc.in

@@ -142,10 +142,10 @@ SECTIONS
   {
     *(.rsrc)
     *(SORT(.rsrc$*))
-    _SYM (_cygheap_start) = .;
   }
   .cygheap ALIGN(__section_alignment__) :
   {
+    _SYM (_cygheap_start) = .;
 #ifdef __x86_64__
     . = . + (3072 * 1024);
 #else