Replace:

INCLUDEPATH += src/leveldb/include src/leveldb/helpers
LIBS += $$PWD/src/leveldb/libleveldb.a $$PWD/src/leveldb/libmemenv.a
!win32 {
    # we use QMAKE_CXXFLAGS_RELEASE even without RELEASE=1 because we use RELEASE to indicate linking preferences not -O preferences
    genleveldb.commands = cd $$PWD/src/leveldb && CC=$$QMAKE_CC CXX=$$QMAKE_CXX $(MAKE) OPT=\"$$QMAKE_CXXFLAGS $$QMAKE_CXXFLAGS_RELEASE\" libleveldb.a libmemenv.a
} else {
    # make an educated guess about what the ranlib command is called
    isEmpty(QMAKE_RANLIB) {
        QMAKE_RANLIB = $$replace(QMAKE_STRIP, strip, ranlib)
    }
    LIBS += -lshlwapi
    genleveldb.commands = cd $$PWD/src/leveldb && CC=$$QMAKE_CC CXX=$$QMAKE_CXX TARGET_OS=OS_WINDOWS_CROSSCOMPILE $(MAKE) OPT=\"$$QMAKE_CXXFLAGS $$QMAKE_CXXFLAGS_RELEASE\" libleveldb.a libmemenv.a && $$QMAKE_RANLIB $$PWD/src/leveldb/libleveldb.a && $$QMAKE_RANLIB $$PWD/src/leveldb/libmemenv.a
}
genleveldb.target = $$PWD/src/leveldb/libleveldb.a
genleveldb.depends = FORCE
PRE_TARGETDEPS += $$PWD/src/leveldb/libleveldb.a
QMAKE_EXTRA_TARGETS += genleveldb
# Gross ugly hack that depends on qmake internals, unfortunately there is no other way to do it.
QMAKE_CLEAN += $$PWD/src/leveldb/libleveldb.a; cd $$PWD/src/leveldb ; $(MAKE) clean

With:

# LevelDB
INCLUDEPATH += src/leveldb/include src/leveldb/helpers
LIBS += $$PWD/src/leveldb/libleveldb.a $$PWD/src/leveldb/libmemenv.a
!win32 {
    # we use QMAKE_CXXFLAGS_RELEASE even without RELEASE=1 because we use RELEASE to indicate linking preferences not -O preferences
    # genleveldb.commands = cd $$PWD/src/leveldb && CC=$$QMAKE_CC CXX=$$QMAKE_CXX $(MAKE) OPT=\"$$QMAKE_CXXFLAGS $$QMAKE_CXXFLAGS_RELEASE\" libleveldb.a libmemenv.a
} else {
    # make an educated guess about what the ranlib command is called
    isEmpty(QMAKE_RANLIB) {
        QMAKE_RANLIB = $$replace(QMAKE_STRIP, strip, ranlib)
    }
    LIBS += -lshlwapi
    # genleveldb.commands = cd $$PWD/src/leveldb && CC=$$QMAKE_CC CXX=$$QMAKE_CXX TARGET_OS=OS_WINDOWS_CROSSCOMPILE $(MAKE) OPT=\"$$QMAKE_CXXFLAGS $$QMAKE_CXXFLAGS_RELEASE\" libleveldb.a libmemenv.a && $$QMAKE_RANLIB $$PWD/src/leveldb/libleveldb.a && $$QMAKE_RANLIB $$PWD/src/leveldb/libmemenv.a
}
genleveldb.target = $$PWD/src/leveldb/libleveldb.a
genleveldb.depends = FORCE
PRE_TARGETDEPS += $$PWD/src/leveldb/libleveldb.a
QMAKE_EXTRA_TARGETS += genleveldb
# Gross ugly hack that depends on qmake internals, unfortunately there is no other way to do it.
QMAKE_CLEAN += $$PWD/src/leveldb/libleveldb.a; cd $$PWD/src/leveldb ; $(MAKE) clean