qt-everywhere-src-5.14.1/qtbase/mkspecs/features/static_runtime.prf

msvc {
    # -MD becomes -MT, -MDd becomes -MTd
    QMAKE_CFLAGS ~= s,^-MD(d?)$,-MT\\1,g
    QMAKE_CXXFLAGS ~= s,^-MD(d?)$,-MT\\1,g
} else: mingw {
    QMAKE_LFLAGS += -static
}