AVR: Skip some test cases that don't work for it.

gcc/testsuite/
	* gcc.c-torture/execute/ieee/cdivchkd.x: New file.
	* gcc.c-torture/execute/ieee/cdivchkf.x: New file.
	* gcc.dg/flex-array-counted-by.c: Require wchar.
	* gcc.dg/fold-copysign-1.c [avr]: Add -mdouble=64.

gcc/testsuite/gcc.c-torture/execute/ieee/cdivchkd.x

@@ -0,0 +1,5 @@
+if [istarget "avr-*-*"] {
+    # Floating-point support is incomplete.
+    return 1
+}
+return 0

gcc/testsuite/gcc.c-torture/execute/ieee/cdivchkf.x

@@ -0,0 +1,5 @@
+if [istarget "avr-*-*"] {
+    # Floating-point support is incomplete.
+    return 1
+}
+return 0

gcc/testsuite/gcc.dg/flex-array-counted-by.c

@@ -1,6 +1,7 @@
 /* Testing the correct usage of attribute counted_by.  */   
 /* { dg-do compile } */
 /* { dg-options "-O2" } */
+/* { dg-require-effective-target wchar } */
 
 #include <wchar.h>
 

gcc/testsuite/gcc.dg/fold-copysign-1.c

@@ -1,6 +1,7 @@
 /* { dg-do compile } */
 /* { dg-options "-O -fdump-tree-cddce1" } */
 /* { dg-additional-options "-msse -mfpmath=sse" { target { { i?86-*-* x86_64-*-* } && ilp32 } } } */
+/* { dg-additional-options "-mdouble=64" { target { avr-*-* } } } */
 
 double foo (double x)
 {