This make is now invoked from each individual target make with the
appropriate CC and EXTRA_CFLAGS set for each guest. It then includes
additional Makefile.targets from:

  - tests/tcg/multiarch (always)
  - tests/tcg/$(TARGET_BASE_ARCH) (if available)
  - tests/tcg/$(TARGET_NAME)

The order is important as the later Makefile's may want to suppress
TESTS from its base arch profile. Each included Makefile.target is
responsible for adding TESTS as well as defining any special build
instructions for individual tests.
Signed-off-by: NAlex Bennée <alex.bennee@linaro.org>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>