avr: Fix ICE on optimize attribute.

This commit fixes an ICE when an optimize attribute changes the prevailing
optimization level.

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105069 describes the
same ICE for the sh target, where the fix was to enable save/restore of
target specific options modified via TARGET_OPTIMIZATION_TABLE hook.

For the AVR target, mgas-isr-prologues and -mmain-is-OS_task are those
target specific options. As they enable generation of more optimal code,
this commit adds the Optimization option property to those option records,
and that fixes the ICE.

Regression run shows no regressions, and >100 new PASSes.

	PR target/110086

gcc/ChangeLog:

	* config/avr/avr.opt (mgas-isr-prologues, mmain-is-OS_task):
	Add Optimization option property.

gcc/testsuite/ChangeLog:

	* gcc.target/avr/pr110086.c: New test.

gcc/config/avr/avr.opt

@@ -27,7 +27,7 @@ Target RejectNegative Joined Var(avr_mmcu) MissingArgError(missing device or arc
 -mmcu=MCU	Select the target MCU.
 
 mgas-isr-prologues
-Target Var(avr_gasisr_prologues) UInteger Init(0)
+Target Var(avr_gasisr_prologues) UInteger Init(0) Optimization 
 Allow usage of __gcc_isr pseudo instructions in ISR prologues and epilogues.
 
 mn-flash=
@@ -65,7 +65,7 @@ Target Joined RejectNegative UInteger Var(avr_branch_cost) Init(0)
 Set the branch costs for conditional branch instructions.  Reasonable values are small, non-negative integers.  The default branch cost is 0.
 
 mmain-is-OS_task
-Target Mask(MAIN_IS_OS_TASK)
+Target Mask(MAIN_IS_OS_TASK) Optimization
 Treat main as if it had attribute OS_task.
 
 morder1

gcc/testsuite/gcc.target/avr/pr110086.c

@@ -0,0 +1,5 @@
+/* { dg-do compile } */
+/* { dg-options "-Os" } */
+
+void __attribute__((optimize("O0"))) foo() {
+}