While trying to reduce the PR64835 case for ARM and x86, I noticed that 
the alignment flags are cleared for x86 when attribute optimized is used.

With the attached testcases, the visible effects are twofold :

1) Functions compiled in with attribute optimize (-O2) are not aligned 
as if they were with the -O2 flag.

2) can_inline_edge_p fails because opts_for_fn (caller->decl) != 
opts_for_fn (callee->decl)) even-though they are compiled with the same 
optimization level.

indeed we have:

  <optimization_node 0x7ffff7522000
     align_functions (0x10)
     align_jumps (0x10)
     align_loops (0x10)
     flag_sched_stalled_insns_dep (0x1)
     flag_tree_parallelize_loops (0x1)
     flag_fp_contract_mode (0x2)
     flag_ira_algorithm (0)
     flag_ira_region (0x2)
     flag_simd_cost_model (0)
     flag_vect_cost_model (0x1)
     optimize (0x2)
     flag_aggressive_loop_optimizations (0x1)
     ...

<optimization_node 0x7ffff7522188
     flag_sched_stalled_insns_dep (0x1)
     flag_tree_parallelize_loops (0x1)
     flag_fp_contract_mode (0x2)
     flag_ira_algorithm (0)
     flag_ira_region (0x2)
     flag_simd_cost_model (0)
     flag_vect_cost_model (0x1)
     optimize (0x2)
     flag_aggressive_loop_optimizations (0x1)
     ...

The problem is that the alignment flags are not recomputed when setting 
the attribute flags in DECL_FUNCTION_SPECIFIC_OPTIMIZATION. Implementing 
the TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE hook to set them fixes the problem.

NB: TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE is also used to hold options 
from attribute target, so.this patch is a prerequisite to fix PR/64835 
on ARM and x86

bootstrapped, regtested with no new failures for x86_64-unknown-linux-gnu

Comments ? I'd like to candidate this for trunk when stage1 opens again.

Many Thanks

Christian