qmake fails assertion when building on Mac's /tmp dir

./configure -v -prefix /tmp/qt-inst -opensource -release -confirm-license -no-c++11
[...]
ASSERT: "uint(i) < uint(size())" in file /tmp/qtbase-opensource-src-5.1.0-rc2/include/QtCore/../../src/corelib/tools/qstring.h, line 737
/tmp/qtbase-opensource-src-5.1.0-rc2/config.tests/unix/compile.test: line 78:  7998 Abort trap: 6           OUTDIR=$OUTDIR "$@"

/tmp/qtbase-opensource-src-5.1.0-rc2/bin/qmake -nocache -spec /tmp/qtbase-opensource-src-5.1.0-rc2/mkspecs/macx-clang CONFIG+= CONFIG+=android_app CONFIG-=debug_and_release LIBS*= LIBS+= INCLUDEPATH*= QMAKE_CXXFLAGS*= QMAKE_CXXFLAGS+= QT_BUILD_TREE=/tmp/qtbase-opensource-src-5.1.0-rc2 /tmp/qtbase-opensource-src-5.1.0-rc2/config.tests/unix/floatmath/floatmath.pro -o /tmp/qtbase-opensource-src-5.1.0-rc2/config.tests/unix/floatmath/Makefile

#0  0x00007fff8e5f0212 in __pthread_kill ()
#1  0x00007fff8a585b54 in pthread_kill ()
#2  0x00007fff8a5c9dce in abort ()
#3  0x000000010031bcc8 in qt_message_fatal (context=@0x7fff5fbfefd8, message=@0x7fff5fbfefa8) at /tmp/qtbase-opensource-src-5.1.0-rc2/src/corelib/global/qlogging.cpp:944
#4  0x000000010031c573 in QMessageLogger::fatal (this=0x7fff5fbfefd8, msg=0x1003cb3ce "ASSERT: \"%s\" in file %s, line %d") at /tmp/qtbase-opensource-src-5.1.0-rc2/src/corelib/global/qlogging.cpp:360
#5  0x000000010021332a in qt_assert (assertion=0x1003bf85a "uint(i) < uint(size())", file=0x1003be932 "/tmp/qtbase-opensource-src-5.1.0-rc2/include/QtCore/../../src/corelib/tools/qstring.h", line=737) at /tmp/qtbase-opensource-src-5.1.0-rc2/src/corelib/global/qglobal.cpp:2014
#6  0x0000000100016395 in QString::at (this=0x7fff5fbff130, i=-1) at qstring.h:737
#7  0x000000010001c43e in QMakeGlobals::setDirectories (this=0x7fff5fbff680, input_dir=@0x7fff5fbff1d0, output_dir=@0x1004c19f8) at /tmp/qtbase-opensource-src-5.1.0-rc2/qmake/library/qmakeglobals.cpp:252
#8  0x000000010000a3b6 in Option::prepareProject (pfile=@0x7fff5fbff430) at /tmp/qtbase-opensource-src-5.1.0-rc2/qmake/option.cpp:467
#9  0x0000000100014b68 in runQMake (argc=16, argv=0x7fff5fbff750) at /tmp/qtbase-opensource-src-5.1.0-rc2/qmake/main.cpp:168
#10 0x00000001000151a2 in main (argc=16, argv=0x7fff5fbff750) at /tmp/qtbase-opensource-src-5.1.0-rc2/qmake/main.cpp:207

#7  0x000000010001c43e in QMakeGlobals::setDirectories (this=0x7fff5fbff680, input_dir=@0x7fff5fbff1d0, output_dir=@0x1004c19f8) at /tmp/qtbase-opensource-src-5.1.0-rc2/qmake/library/qmakeglobals.cpp:252
252             while (++lastSl, srcpath.at(--srcLen) == dstpath.at(--dstLen))
(gdb) i lo
srcpath = {
  d = 0x100c08f30
}
dstLen = -1
dstpath = {
  d = 0x100c09260
}
srcLen = 7
lastSl = 1
(gdb) x/73hc ((char*)srcpath.d)+24
0x100c08f48:    47 '/'  112 'p' 114 'r' 105 'i' 118 'v' 97 'a'  116 't' 101 'e'
0x100c08f58:    47 '/'  116 't' 109 'm' 112 'p' 47 '/'  113 'q' 116 't' 98 'b'
0x100c08f68:    97 'a'  115 's' 101 'e' 45 '-'  111 'o' 112 'p' 101 'e' 110 'n'
0x100c08f78:    115 's' 111 'o' 117 'u' 114 'r' 99 'c'  101 'e' 45 '-'  115 's'
0x100c08f88:    114 'r' 99 'c'  45 '-'  53 '5'  46 '.'  49 '1'  46 '.'  48 '0'
0x100c08f98:    45 '-'  114 'r' 99 'c'  50 '2'  47 '/'  99 'c'  111 'o' 110 'n'
0x100c08fa8:    102 'f' 105 'i' 103 'g' 46 '.'  116 't' 101 'e' 115 's' 116 't'
0x100c08fb8:    115 's' 47 '/'  117 'u' 110 'n' 105 'i' 120 'x' 47 '/'  102 'f'
0x100c08fc8:    108 'l' 111 'o' 97 'a'  116 't' 109 'm' 97 'a'  116 't' 104 'h'
0x100c08fd8:    47 '/'
(gdb) x/65hc ((char*)srcpath.d)+24
0x100c08f48:    47 '/'  112 'p' 114 'r' 105 'i' 118 'v' 97 'a'  116 't' 101 'e'
0x100c08f58:    47 '/'  116 't' 109 'm' 112 'p' 47 '/'  113 'q' 116 't' 98 'b'
0x100c08f68:    97 'a'  115 's' 101 'e' 45 '-'  111 'o' 112 'p' 101 'e' 110 'n'
0x100c08f78:    115 's' 111 'o' 117 'u' 114 'r' 99 'c'  101 'e' 45 '-'  115 's'
0x100c08f88:    114 'r' 99 'c'  45 '-'  53 '5'  46 '.'  49 '1'  46 '.'  48 '0'
0x100c08f98:    45 '-'  114 'r' 99 'c'  50 '2'  47 '/'  99 'c'  111 'o' 110 'n'
0x100c08fa8:    102 'f' 105 'i' 103 'g' 46 '.'  116 't' 101 'e' 115 's' 116 't'
0x100c08fb8:    115 's' 47 '/'  117 'u' 110 'n' 105 'i' 120 'x' 47 '/'  102 'f'
0x100c08fc8:    108 'l'