Apply #ifdef/#ifndef where possible

Marlin/src/HAL/HAL_DUE/usb/compiler.h

Marlin/src/HAL/HAL_DUE/usb/osc.h

Marlin/src/HAL/HAL_DUE/usb/spc_protocol.h

Marlin/src/HAL/HAL_DUE/usb/udi_cdc.h

Marlin/src/HAL/HAL_DUE/usb/udi_cdc_conf.h

Marlin/src/HAL/HAL_STM32F1/SPI.h

Marlin/src/inc/SanityCheck.h

...extensible_ui/lib/lulzbot/ftdi_eve_lib/basic/ftdi_basic.h

.../lcd/extensible_ui/lib/lulzbot/ftdi_eve_lib/basic/spi.cpp

...rc/lcd/extensible_ui/lib/lulzbot/ftdi_eve_lib/basic/spi.h

...n/src/lcd/extensible_ui/lib/lulzbot/ftdi_eve_lib/compat.h

...ible_ui/lib/lulzbot/ftdi_eve_lib/extended/ftdi_extended.h

Marlin/src/lcd/extensible_ui/lib/lulzbot/screens/screens.h

Marlin/src/pins/lpc1768/pins_RAMPS_RE_ARM.h

Marlin/src/pins/ramps/pins_Z_BOLT_X_SERIES.h

Marlin/src/sd/usb_flashdrive/lib-uhs2/settings.h

...ive/lib-uhs3/UHS_host/UHS_BULK_STORAGE/UHS_BULK_STORAGE.h

Marlin/src/sd/usb_flashdrive/lib-uhs3/UHS_host/UHS_UsbCore.h

Marlin/src/sd/usb_flashdrive/lib-uhs3/UHS_host/UHS_address.h

Marlin/src/sd/usb_flashdrive/lib-uhs3/UHS_host/UHS_host.h