In order to compile PHP on 64 bit you need to use the option --with-libdir=lib64 otherwise you will stay forever with the following error

checking for MySQL support... yes
checking for specified location of the MySQL UNIX socket... no
checking for MySQL UNIX socket location... no
checking for mysql_close in -lmysqlclient... no
checking for mysql_error in -lmysqlclient... no
configure: error: mysql configure failed. Please check config.log for more information.

Other possible reasons are :
1. missing the libtool-ltdl-devel package
2. missing the ncurses-devel
3. missing mysql-devel package

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