Bison 3.5.91 with older Flex

[Bruno Haible]

When a flex version < 2.6.4 is in $PATH, bison fails to build.

More precisely, the configuration fails:
...
checking for flex... flex
checking whether lex is flex... yes
checking lex output file root... lex.yy
checking lex library... -lfl
checking whether yytext is a pointer... yes
...
config.status: executing tests/atconfig commands
  LEX      examples/c/reccalc/scan.stamp
flex: unknown flag '-'.  For usage, try
        flex --help
gmake: *** [Makefile:9998: examples/c/reccalc/scan.stamp] Error 1
  LEX      examples/c/reccalc/scan.stamp
flex: unknown flag '-'.  For usage, try
        flex --help
gmake: *** [Makefile:9998: examples/c/reccalc/scan.stamp] Error 1
$ flex --version
flex version 2.5.4
$ grep -i flex config.status 
S["FLEX_CXX_WORKS_FALSE"]="#"
S["FLEX_CXX_WORKS_TRUE"]=""
S["FLEX_WORKS_FALSE"]="#"
S["FLEX_WORKS_TRUE"]=""
S["LEX_IS_FLEX"]="true"
S["LEX"]="flex"
S["FLEX_SCANNER_CXXFLAGS"]=""

I don't know what the flex command is that the config.status attempts to
execute (because you chose to hide it). Most probably it contains options
that flex 2.5.4 does not understand.

$ flex --help
flex [-bcdfhilnpstvwBFILTV78+? -C[aefFmr] -ooutput -Pprefix -Sskeleton]
        [--help --version] [file ...]
        -b  generate backing-up information to lex.backup
        -c  do-nothing POSIX option
        -d  turn on debug mode in generated scanner
        -f  generate fast, large scanner
        -h  produce this help message
        -i  generate case-insensitive scanner
        -l  maximal compatibility with original lex
        -n  do-nothing POSIX option
        -p  generate performance report to stderr
        -s  suppress default rule to ECHO unmatched text
        -t  write generated scanner on stdout instead of lex.yy.c
        -v  write summary of scanner statistics to f
        -w  do not generate warnings
        -B  generate batch scanner (opposite of -I)
        -F  use alternative fast scanner representation
        -I  generate interactive scanner (opposite of -B)
        -L  suppress #line directives in scanner
        -T  flex should run in trace mode
        -V  report flex version
        -7  generate 7-bit scanner
        -8  generate 8-bit scanner
        -+  generate C++ scanner class
        -?  produce this help message
        -C  specify degree of table compression (default is -Cem):
                -Ca  trade off larger tables for better memory alignment
                -Ce  construct equivalence classes
                -Cf  do not compress scanner tables; use -f representation
                -CF  do not compress scanner tables; use -F representation
                -Cm  construct meta-equivalence classes
                -Cr  use read() instead of stdio for scanner input
        -o  specify output filename
        -P  specify scanner prefix other than "yy"
        -S  specify skeleton file
        --help     produce this help message
        --version  report flex version

$ cd examples/c/reccalc/

$ grep -i flex Makefile local.mk 
Makefile:FLEX = flex
Makefile:       $(FLEX) $(FLEXFLAGS) -o$*.c --header-file=$*.h $<
local.mk:if FLEX_WORKS
local.mk:endif FLEX_WORKS

Apparently the --header-file option is not supported.

Indeed: https://github.com/westes/flex/blob/master/NEWS
shows that the option --header was introduced in version 2.5.6.
And 
https://github.com/westes/flex/commit/56a530abf7e16ce35ea36748ff2e86f2f0022bc2
shows that the option --header-file was introduced in version 2.6.4.

Bruno