Fixes compiler warning
test-unicode.c:589:1: warning: ‘test_unicode_properties_lenient’ defined but not used
which didn't happen with autotools.
Reason it does with meson is that the setup for C was slightly wrong.
We would only add -DHAVE_CONFIG_H to cpp_args which is only valid when
compiling C++ code, but not plain C code, and many of these tests were
plain C.
Instead pass -DHAVE_CONFIG_H via add_project_arguments() and make sure
to set both c_args and cpp_args when building test executables.
Fixes https://github.com/harfbuzz/harfbuzz/issues/2257
Ebrahim Byagowi
Tim-Philipp Müller
Khaled Hosny
Mathieu Duponchelle