AIX compile report:

+ libxml2-2.6.11
+ gcc
+ AIX 5.1 on RS6000

* configure all went well

* make:
encoding.c: In function `xmlIconvWrapper':
encoding.c:1664: warning: passing arg 2 of `iconv' from incompatible pointer type

debugXML.c: In function `xmlDebugDumpDtdNode':
debugXML.c:76: warning: format not a string literal, argument types not checked
debugXML.c: In function `xmlDebugDumpAttrDecl':
debugXML.c:130: warning: format not a string literal, argument types not checked
debugXML.c: In function `xmlDebugDumpElemDecl':
debugXML.c:251: warning: format not a string literal, argument types not checked
debugXML.c: In function `xmlDebugDumpEntityDecl':
debugXML.c:329: warning: format not a string literal, argument types not checked
debugXML.c:366: warning: format not a string literal, argument types not checked
debugXML.c:370: warning: format not a string literal, argument types not checked
debugXML.c:374: warning: format not a string literal, argument types not checked
debugXML.c:378: warning: format not a string literal, argument types not checked
debugXML.c: In function `xmlDebugDumpNamespace':
debugXML.c:418: warning: format not a string literal, argument types not checked
debugXML.c: In function `xmlDebugDumpEntity':
debugXML.c:461: warning: format not a string literal, argument types not checked
debugXML.c:488: warning: format not a string literal, argument types not checked
debugXML.c:492: warning: format not a string literal, argument types not checked
debugXML.c:496: warning: format not a string literal, argument types not checked
debugXML.c:500: warning: format not a string literal, argument types not checked
debugXML.c: In function `xmlDebugDumpAttr':
debugXML.c:524: warning: format not a string literal, argument types not checked
debugXML.c: In function `xmlDebugDumpOneNode':
debugXML.c:598: warning: format not a string literal, argument types not checked
debugXML.c:604: warning: format not a string literal, argument types not checked
debugXML.c:614: warning: format not a string literal, argument types not checked
debugXML.c:618: warning: format not a string literal, argument types not checked
debugXML.c:625: warning: format not a string literal, argument types not checked
debugXML.c:629: warning: format not a string literal, argument types not checked
debugXML.c:633: warning: format not a string literal, argument types not checked
debugXML.c:637: warning: format not a string literal, argument types not checked
debugXML.c:641: warning: format not a string literal, argument types not checked
debugXML.c:646: warning: format not a string literal, argument types not checked
debugXML.c:650: warning: format not a string literal, argument types not checked
debugXML.c:654: warning: format not a string literal, argument types not checked
debugXML.c:658: warning: format not a string literal, argument types not checked
debugXML.c:677: warning: format not a string literal, argument types not checked
debugXML.c:681: warning: format not a string literal, argument types not checked
debugXML.c:685: warning: format not a string literal, argument types not checked
debugXML.c:690: warning: format not a string literal, argument types not checked
debugXML.c:701: warning: format not a string literal, argument types not checked
debugXML.c: In function `xmlDebugDumpNode':
debugXML.c:761: warning: format not a string literal, argument types not checked

xpath.c: In function `xmlXPathDebugDumpNode':
xpath.c:648: warning: format not a string literal, argument types not checked
xpath.c:656: warning: format not a string literal, argument types not checked
xpath.c: In function `xmlXPathDebugDumpNodeList':
xpath.c:673: warning: format not a string literal, argument types not checked
xpath.c: In function `xmlXPathDebugDumpNodeSet':
xpath.c:696: warning: format not a string literal, argument types not checked
xpath.c:705: warning: format not a string literal, argument types not checked
xpath.c: In function `xmlXPathDebugDumpValueTree':
xpath.c:722: warning: format not a string literal, argument types not checked
xpath.c:728: warning: format not a string literal, argument types not checked
xpath.c: In function `xmlXPathDebugDumpLocationSet':
xpath.c:743: warning: format not a string literal, argument types not checked
xpath.c:750: warning: format not a string literal, argument types not checked
xpath.c: In function `xmlXPathDebugDumpObject':
xpath.c:774: warning: format not a string literal, argument types not checked
xpath.c:829: warning: format not a string literal, argument types not checked
xpath.c:837: warning: format not a string literal, argument types not checked
xpath.c:844: warning: format not a string literal, argument types not checked
xpath.c: In function `xmlXPathDebugDumpStepOp':
xpath.c:877: warning: format not a string literal, argument types not checked
xpath.c: In function `xmlXPathDebugDumpCompExpr':
xpath.c:1062: warning: format not a string literal, argument types not checked
xpath.c: At top level:
trionan.c:217: warning: `trio_is_negative' defined but not used
nanoftp.c: In function `xmlNanoFTPGetConnection':
nanoftp.c:1558: structure has no member named `ss_family'
nanoftp.c:1577: structure has no member named `ss_family'
nanoftp.c:1608: structure has no member named `ss_family'
nanoftp.c:1645: structure has no member named `ss_family'
nanoftp.c:1664: structure has no member named `ss_family'
make: 1254-004 The error code from the last command is 1.


Stop.
make: 1254-004 The error code from the last command is 1.


Stop.
make: 1254-004 The error code from the last command is 2.


Stop.


Based on a hint I saw in an email archive, I tried 
  ./config --disable-ipv6
and everything successfully compiled [with the same warnings as before].