txr: Depends on bison and flex for Linuxbrew
txr: Depends on bison and flex for Linuxbrew

Fix errors:
* Checking for yacc program ... not found
* /bin/bash: flex: command not found

Closes Linuxbrew/homebrew-core#148.

Closes Linuxbrew/homebrew-core#3821.

Signed-off-by: Bob W. Hogg <c772a964fd55352a3510e5d535dd9ccc9ac30168@linux.com>

maxim-belkin/homebrew-core,LinuxbrewTestBot/homebrew-core,maxim-belkin/homebrew-core,rwhogg/homebrew-core,Linuxbrew/homebrew-core,rwhogg/homebrew-core,LinuxbrewTestBot/homebrew-core,Linuxbrew/homebrew-core