Please try using this CVS snapshot:

  http://snaps.php.net/php4-latest.tar.gz
 
For Windows:
 
  http://snaps.php.net/win32/php4-win32-latest.zip

Same thing.
-----

pwd && ./configure --enable-trans-sid --with-mysql=/usr/local/mysql --with-apxs2=/usr/local/apache2/bin/apxs --with-gd=/usr/local --with-jpeg-dir=/usr/local --with-png-dir=/usr/local --with-zlib-dir=/usr
/usr/home/evan/php4-200212020630
loading cache ./config.cache
checking for Cygwin environment... no
checking for mingw32 environment... no
checking for working sed... sed
checking host system type... sparc-sun-solaris2.8
checking for gcc... gcc
checking whether the C compiler (gcc  ) works... yes
checking whether the C compiler (gcc  ) is a cross-compiler... no
checking whether we are using GNU C... yes
checking whether gcc accepts -g... yes
checking whether gcc and cc understand -c and -o together... yes
checking how to run the C preprocessor... gcc -E
checking for AIX... no
checking if compiler supports -R... yes
checking for ranlib... ranlib
checking whether ln -s works... yes
checking for gawk... gawk
checking for bison... no
checking for byacc... no
configure: warning: You will need bison if you want to regenerate the PHP parsers.
checking for flex... lex
checking for yywrap in -ll... yes
checking lex output file root... lex.yy
checking whether yytext is a pointer... no
checking for working const... yes
checking flex version... lex: Software Generation Utilities (SGU) Solaris-ELF (4.0)

And it justs hangs again. The solaris version of lex prints it's version on standard err and then enters processing mode, so like most solaris things you just need to cater to the way it works. Echoing nothing to $LEX -V, while dumping a lot of garbage on the screen, allows configure to continue and still works with GNU flex install as well.

Here's a unified diff.

--- configure.bak       Mon Dec  2 02:16:42 2002
+++ configure   Mon Dec  2 02:32:16 2002
@@ -2632,7 +2632,7 @@
 
 echo $ac_n "checking flex version""... $ac_c" 1>&6
 echo "configure:2635: checking flex version" >&5
-set `$LEX -V | grep 'version' | cut -d ' ' -f 3 | sed -e 's/\./ /g' | sed -e 's/^0-9 //g'`
+set `echo '' | $LEX -V | grep 'version' | cut -d ' ' -f 3 | sed -e 's/\./ /g' | sed -e 's/^0-9 //g'`
 if test "${1}" != "2" -o "${2}" != "5" -o "${3}" -lt "4"; then
         echo "configure: warning: You will need flex 2.5.4 or later if you want to regenerate Zend/PHP lexical parsers." 1>&2
 fi

This bug has been fixed in CVS.

In case this was a PHP problem, snapshots of the sources are packaged
every three hours; this change will be in the next snapshot. You can
grab the snapshot at http://snaps.php.net/.
 
In case this was a documentation problem, the fix will show up soon at
http://www.php.net/manual/.

In case this was a PHP.net website problem, the change will show
up on the PHP.net site and on the mirror sites in short time.
 
Thank you for the report, and for helping us make PHP better.

The fix just didn't make it into the snapshot yet, but the same thing was added as your patch is.