AM_PROG_LEX can't handle situation when flex installed, but libfl.a not

[Basin Ilya]

Hi.
In RHEL 6.6 and later they moved libfl.a into the separate package
"flex-devel", available only to subscribers. "flex" package is still on
RHEL DVD and part of 'Development Tools' group.

See https://rhn.redhat.com/errata/RHBA-2014-1402.html

When configure run on systems without flex-devel, but with 'Development
Tools' installed, the result is:

    checking for flex... flex
    checking lex output file root... lex.yy
    checking lex library... none needed
    checking whether yytext is a pointer... no

After installing flex-devel it's:

    checking for flex... flex
    checking lex output file root... lex.yy
    checking lex library... -lfl
    checking whether yytext is a pointer... yes

I created the configure script with fairly recent autoconf 2.69 from
ArchLinux.


I think the check should not be successful unless it finds a way to
compile a test program with CC (currently _all_ compilations fail with
either "cannot find -lfl" or "undefined reference to `yywrap'")

Maybe it could try whether flex supports "--noyywrap".