'=~' crash on NetBSD

[Martijn Dekker]

On NetBSD, bash (all versions, including current git) dumps core when 
using [[ to match against an ERE containing certain UTF-8 characters, 
for example, É ($'\303\211').

| $ bin/bash-5.0-debug -c "[[ c =~ $'\303\211' ]]"
|
| malloc: unknown:0: assertion botched
| malloc: 0x81ba08: allocated: last allocated from unknown:0
| free: start and end chunk sizes differ
| Aborting...Abort trap (core dumped)

If it helps, here's a backtrace generated from the core file by 'gdb'. 
It seems to suggest that only the first byte of the UTF-8 character is 
included in the pattern...

#0  0x00007ae3a22fe48a in _lwp_kill () from /usr/lib/libc.so.12
#1  0x00007ae3a22fdd32 in abort () from /usr/lib/libc.so.12
#2  0x000000000043492e in programming_error (
    format=0x5213d8 "free: start and end chunk sizes differ")
    at error.c:175
#3  0x00000000004f3e78 in xbotch (mem=0x81ba08, e=8,
    s=0x5213d8 "free: start and end chunk sizes differ", file=0x0, line=0)
    at malloc.c:358
#4  0x00000000004f4e40 in internal_free (mem=0x81ba08, file=0x0, line=0,
    flags=0) at malloc.c:964
#5  0x00000000004f5a1e in free (mem=0x81ba08) at malloc.c:1392
#6  0x00000000004b3c02 in sh_regmatch (string=0x806358 "c",
    pattern=0x819d28 "\303", flags=3) at shmatch.c:118
#7  0x0000000000424c28 in execute_cond_node (cond=0x819a48)
    at execute_cmd.c:3884
#8  0x0000000000424e3f in execute_cond_command (cond_command=0x819a48)
    at execute_cmd.c:3959
#9  0x000000000041fb34 in execute_command_internal (command=0x819a88,
    asynchronous=0, pipe_in=-1, pipe_out=-1, fds_to_close=0x8199e8)
    at execute_cmd.c:1029
#10 0x0000000000492b38 in parse_and_execute (
    string=0x805188 "[[ c =~ \303 ]]", from_file=0x4fe190 "-c", flags=4)
    at evalstring.c:460
#11 0x0000000000406452 in run_one_command (
    command=0x7f7fffb6ca46 "[[ c =~ \303 ]]") at shell.c:1436
#12 0x00000000004055f8 in main (argc=3, argv=0x7f7fffb6c468,
    env=0x7f7fffb6c488) at shell.c:738


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