Add the Phobos v3 unit tests to the regular unittest build.

This probably isn't the best way to do this, and presumably, it'll need
to be reworked at some point (just like the Phobos v3 build in general
likely will need to be reworked), but this should at least make it so
that the Phobos v3 tests get run as part of the CI.

Makefile

@@ -344,6 +344,7 @@ else
 unittest : unittest-debug unittest-release
 unittest-%:
 	$(MAKE) unittest OS=$(OS) MODEL=$(MODEL) DMD=$(DMD) BUILD=$*
+	dub test --build=unittest-$*
 endif
 
 ################################################################################

dub.sdl

@@ -18,3 +18,11 @@ configuration "unittest" {
     targetPath "generated-lib"
     #excludedSourceFiles "unittest.d" "test/**" "std/**" "tools/**" "etc/**"
 }
+
+buildType "unittest-debug" {
+    buildOptions "unittests" "debugMode" "debugInfo"
+}
+
+buildType "unittest-release" {
+    buildOptions "unittests" "releaseMode" "optimize"
+}