tesseract @3.04.00_2 build failure: 'unordered_map' file not found

[alexmptrac@…]

MacOS version: 10.7.5 XCode version: 4.6.3

Tesseract @3.04.00_2 is failing to install on two machines here, both running Lion. This problem came up as part of a routine 'port upgrade outdated' (previous versions of tesseract worked OK on these systems).

Googling for the compiler error found this page, which sounds relevant, though it isn't clear to me what to do to fix the problem: ​http://stackoverflow.com/questions/26233011/what-could-cause-clang-to-not-find-the-unordered-map-header