configure stops

creating cache ./config.cache checking host system type... i686-pc-linux-gnu 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... no checking if compiler supports -Wl,-rpath,... yes checking for re2c... exit 0; checking whether ln -s works... yes checking for gawk... gawk checking for bison... bison -y checking bison version... configure: warning: You will need bison 1.28, 1.35, 1.75 or 1.875 if you want to regenerate the Zend parser (found 2.0). 2.0 (ok) checking for flex... flex checking for yywrap in -lfl... yes checking lex output file root... running top on another session flex is taking up 99.8% of the CPU, any thoughts as to get around this.