[PATCH] Work around in-tree gmp configure problems

[Bernd Edlinger <bernd dot edlinger at hotmail dot de>]

Hi,

since r217627 we use an updated AutoMake "missing" script.  However that revealed a hidden
bug in gmp-4.3.2's (up to gmp-6.0.0a) configure script.  That is: an in-tree gmp/configure fails
now if flex is missing.  The gmp configure uses our missing flex script, and previously that emitted
an error message and created a dummy lex.yy.c, The new version of that script does no longer create
any lex.yy.c.

But also if flex is installed, the configure script sets M4=m4-not-needed, before calling flex,
which aborts, and leaves an empty lex.yy.c.  However chances are that the flex tool fails in a way
that there is no lex.yy.c at all, for instance under windows, or with a different version of flex.

Now the problem is, if the invocation of flex does not create at least an empty lex.yy.c the whole
gmp configuration fails, even though, flex is only needed for one demo example.

This patch adds LEX="touch lex.yy.c" to the in-tree gmp configure script, which does in fact the
same thing as the flex tool when called under these conditions.

I have tested gmp-4.3.2 and gmp-6.0.0a in-tree and boot-strapped under x86_64-linux-gnu successfully.


OK for trunk?


Thanks
Bernd.

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