double-free complaints in qmake

When running configure for 4.8 or master, I get loads of these messages:

qmake(46866,0xa00ba540) malloc: *** error for object 0xbfffb100: pointer being freed was not allocated

The cause for them is that the makefile for qmake contains the following around line 39:

export MACOSX_DEPLOYMENT_TARGET = 10.4

If you change this to 10.5, the error disappears. It looks like this import forces an older/different realpath(3) to be used. See also stdlib.h line 226 (Snow Leopard).