Fix bash misscompilation with latest bison

[Jan Hubicka]

Hi,

I am having problems with new m4 support.  The bash uses string 
"\"address@hidden""
to pass into function call (that is later expanded in the standard way
as $@ in bash).  M4 interprets $@ as argument and thus the string comes
out as \"\""\".

I didn't found any way how to escape $ in m4 macro cleanly, only way I
found is the suggestion from manual, to simply parenthese the operand
and close parenthesis and open it again just after $, as m4 pass all
unrecognized $ combination trought.

Parenthesis are overwriten into [ .. ]  by bison m4 preambule, so I
replace every $ occuring in string literal or comment of input template
by $][ that will hopefully open and close the parethesis assuming that
they come out parenthesed in all cases.  I tried some cases and it seems
to work.  However $ is not the only special purpose character in m4.  I
believe at least @ can also cause problems.  [] are already escaped into
"trigraphs" by bison looking like @:>@ and later postprocesed from m4
output, that looks also broken to me, as passing @:>@ will get magically
converted into ].

I am attaching the testcase and fix I made

Honza

bisf
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t.y
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