IPA: prevent an UBSAN error

IPA: prevent an UBSAN error

Prevents the following UBSAN error:

./xgcc -B. /home/marxin/Programming/gcc/gcc/testsuite/g++.dg/torture/pr49770.C -O2 -c
/home/marxin/Programming/gcc2/gcc/ipa-modref-tree.h:482:22: runtime error: load of value 2, which is not a valid value for type 'bool'
    #0 0x1fdb4d1 in modref_tree<int>::merge(modref_tree<int>*, vec<modref_parm_map, va_heap, vl_ptr>*) /home/marxin/Programming/gcc2/gcc/ipa-modref-tree.h:482
    #1 0x1fcadaa in merge_call_side_effects(modref_summary*, gimple*, modref_summary*, bool) /home/marxin/Programming/gcc2/gcc/ipa-modref.c:511
    #2 0x1fcbadd in analyze_call /home/marxin/Programming/gcc2/gcc/ipa-modref.c:642
    #3 0x1fcc061 in analyze_stmt /home/marxin/Programming/gcc2/gcc/ipa-modref.c:732
    #4 0x1fccf31 in analyze_function /home/marxin/Programming/gcc2/gcc/ipa-modref.c:823
    #5 0x1fd17e5 in execute /home/marxin/Programming/gcc2/gcc/ipa-modref.c:1441
    #6 0x25cca6e in execute_one_pass(opt_pass*) /home/marxin/Programming/gcc2/gcc/passes.c:2509
    #7 0x25cd39b in execute_pass_list_1 /home/marxin/Programming/gcc2/gcc/passes.c:2597
    #8 0x25cd450 in execute_pass_list_1 /home/marxin/Programming/gcc2/gcc/passes.c:2598
    #9 0x25cd4ee in execute_pass_list(function*, opt_pass*) /home/marxin/Programming/gcc2/gcc/passes.c:2608
    #10 0x25c7a5a in do_per_function_toporder(void (*)(function*, void*), void*) /home/marxin/Programming/gcc2/gcc/passes.c:1726
    #11 0x25cfa3f in execute_ipa_pass_list(opt_pass*) /home/marxin/Programming/gcc2/gcc/passes.c:2941
    #12 0x173572d in ipa_passes /home/marxin/Programming/gcc2/gcc/cgraphunit.c:2642
    #13 0x17364ee in symbol_table::compile() /home/marxin/Programming/gcc2/gcc/cgraphunit.c:2777
    #14 0x17372d9 in symbol_table::finalize_compilation_unit() /home/marxin/Programming/gcc2/gcc/cgraphunit.c:3022
    #15 0x2a1f00a in compile_file /home/marxin/Programming/gcc2/gcc/toplev.c:485
    #16 0x2a27dc8 in do_compile /home/marxin/Programming/gcc2/gcc/toplev.c:2321
    #17 0x2a283cc in toplev::main(int, char**) /home/marxin/Programming/gcc2/gcc/toplev.c:2460
    #18 0x54f21cd in main /home/marxin/Programming/gcc2/gcc/main.c:39
    #19 0x7ffff6f0de09 in __libc_start_main ../csu/libc-start.c:314
    #20 0x9eac09 in _start (/home/marxin/Programming/gcc2/objdir/gcc/cc1plus+0x9eac09)

gcc/ChangeLog:

	* ipa-modref.c (merge_call_side_effects): Clear modref_parm_map
	fields in the vector.