looks it's automatic
#yum search libxml2-devel
...
libxml2-devel.i686 : Libraries, includes, etc. to develop XML and HTML applications
libxml2-devel.x86_64 : Libraries, includes, etc. to develop XML and HTML applications
...
actually no libxml2-devel
but on 64 bit platform, when
#yum install libxml2-devel
it selects libxml2-devel.x86_64 automatically
if want to install 32 bit library, need specify .i686 explicitly
#yum install libxml2-devel.i686
#yum search libxml2-devel
...
libxml2-devel.i686 : Libraries, includes, etc. to develop XML and HTML applications
libxml2-devel.x86_64 : Libraries, includes, etc. to develop XML and HTML applications
...
actually no libxml2-devel
but on 64 bit platform, when
#yum install libxml2-devel
it selects libxml2-devel.x86_64 automatically
if want to install 32 bit library, need specify .i686 explicitly
#yum install libxml2-devel.i686