compile libXext-1.3.1 problem

[Lee Wei han]

i am trying to build libXext-1.3.1 but i get a error message 


checking for X.Org SGML entities >= 1.8... ./configure: line 18029: syntax error near unexpected token `xorg-sgml-doctools'
./configure: line 18029: `PKG_CHECK_EXISTS(xorg-sgml-doctools m4_ifval([1.8],[>= 1.8]),'


what shall i do, please help
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