編譯安裝完 apr apr-util 之後，安裝httpd-2.4.28的時候報下面的錯誤，然而

./configure --with-apr=/usr/local/apr --with-apr-util=/usr/local/apr-util  --prefix=/usr/local/apache2  --enable-so --enable-ssl --enable-cgi --enable-rewrite --with-zlib --with-pcre  --enable-modules=most --enable-mpms-shared=all

已經指定了安裝路徑，還是出錯。

/usr/local/apr-util/lib/libaprutil-1.so: undefined reference to `XML_GetErrorCode'
/usr/local/apr-util/lib/libaprutil-1.so: undefined reference to `XML_SetEntityDeclHandler'
/usr/local/apr-util/lib/libaprutil-1.so: undefined reference to `XML_ParserCreate'
/usr/local/apr-util/lib/libaprutil-1.so: undefined reference to `XML_SetCharacterDataHandler'
/usr/local/apr-util/lib/libaprutil-1.so: undefined reference to `XML_ParserFree'
/usr/local/apr-util/lib/libaprutil-1.so: undefined reference to `XML_SetUserData'
/usr/local/apr-util/lib/libaprutil-1.so: undefined reference to `XML_StopParser'
/usr/local/apr-util/lib/libaprutil-1.so: undefined reference to `XML_Parse'
/usr/local/apr-util/lib/libaprutil-1.so: undefined reference to `XML_ErrorString'
/usr/local/apr-util/lib/libaprutil-1.so: undefined reference to `XML_SetElementHandler'
collect2: error: ld returned 1 exit status
make[2]: *** [htpasswd] Error 1
make[2]: Leaving directory `/usr/local/httpd-2.4.26/support'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/usr/local/httpd-2.4.26/support'
make: *** [all-recursive] Error 1

#終於在彎彎的一個論壇找到了答案。原來是apr apr-util 用了最新的1.6版本（之前1.6版本在centos7編譯安裝apache沒有問題）

降低了版本，用回1.5版本正常解決。

以上為copy：親測是這個原因