newlib: hoist crt0 install up another dir

Commit dd23de27c8 ("newlib: libc: install
CRT0 straight out of subdir") got rid of the libc/sys/ intermediate for
copying the file up, but the top-level newlib/ dir was still expecting
a libc/crt0.o to exist so it could install.  Update that to also look
for the crt0 file directly under libc/ like we already do for crt1.

newlib/configure

@@ -12442,7 +12442,7 @@ CRT0=
 CRT0_DIR=
 if test "x${have_crt0}" = "xyes"; then
   CRT0=crt0.o
-  CRT0_DIR=libc/
+  CRT0_DIR=libc/sys/${sys_dir}/
 fi
  if test x$have_crt0 = xyes; then
   HAVE_CRT0_TRUE=

newlib/configure.ac

@@ -361,7 +361,7 @@ CRT0=
 CRT0_DIR=
 if test "x${have_crt0}" = "xyes"; then
   CRT0=crt0.o
-  CRT0_DIR=libc/
+  CRT0_DIR=libc/sys/${sys_dir}/
 fi
 AM_CONDITIONAL(HAVE_CRT0, test x$have_crt0 = xyes)
 AC_SUBST(CRT0)