MSP430: Add new methods of finding external MCU data file

MCU data file can now be specified with an environment variable or installed
into a toolchain subdirectory.

2019-11-04  Jozef Lawrynowicz  <jozef.l@mittosystems.com>

gcc/
	* config/msp430/driver-msp430.c
	(msp430_get_linker_devices_include_path): New spec function.
	* config/msp430/msp430-devices.c (msp430_dirname): New function.
	(extract_devices_dir_from_exec_prefix): New function.
	(extract_devices_dir_from_collect_gcc): New function.
	(msp430_check_env_var_for_devices): New function.
	(msp430_check_path_for_devices): Use xstrdup instead of ASTRDUP.
	(parse_devices_csv): Call msp430_check_env_var_for_devices if
	devices.csv was not found using other methods.
	* config/msp430/msp430-devices.h (msp430_check_env_var_for_devices):
	New prototype.
	(msp430_dirname): Likewise.
	* config/msp430/msp430.c (msp430_register_pre_includes): New function.
	* config/msp430/msp430.h (EXTRA_SPEC_FUNCTIONS): Add
	msp430_get_linker_devices_include_path.
	(TARGET_EXTRA_PRE_INCLUDES): Define.
	* doc/invoke.texi: Document new ways of searching for support files.

gcc/testsuite/
	* gcc.target/msp430/devices/csv-using-env-var.c: New test.
	* gcc.target/msp430/devices/csv-using-installed.c: New test.
	* gcc.target/msp430/devices/csv-using-option.c: New test.
	* gcc.target/msp430/devices/devices-main.c: New test source file.
	* gcc.target/msp430/devices/msp430-devices.h: New test.
	* gcc.target/msp430/msp430.exp (msp430_device_permutations_runtest):
	Add special cases for csv-using* tests.
	Define TESTING_HARD_DATA when running tests that use hard-coded device
	data.
	(get_installed_device_data_path): New.
	(msp430_hide_installed_devices_data): New.
	(msp430_restore_installed_devices_data): New.
	(msp430_test_installed_device_data): New.
	(msp430_install_device_data): New.

From-SVN: r277772