feat: proper exports implemented for C++ modules

test/static/fixed_string_test.cpp

@@ -20,11 +20,7 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 // SOFTWARE.
 
-#ifdef MP_UNITS_MODULES
-import mp_units;
-#else
 #include <mp-units/bits/external/fixed_string.h>
-#endif
 
 using namespace mp_units;