Add ODIN_BUILD_PROJECT_NAME and //+build-project-name

This allows for condition inclusion of files, similar to `+build` or `ODIN_BUILD`, but relies on the directory name of the project to be the same as specified

Example:

    odin build foo/bar/baz

    ODIN_BUILD_PROJECT_NAME == "baz"

    //+build_project_name baz

src/build_settings.cpp

@@ -225,6 +225,7 @@ struct BuildContext {
 	String ODIN_VENDOR;  // compiler vendor
 	String ODIN_VERSION; // compiler version
 	String ODIN_ROOT;    // Odin ROOT
+	String ODIN_BUILD_PROJECT_NAME; // Odin main/initial package's directory name
 	bool   ODIN_DEBUG;   // Odin in debug mode
 	bool   ODIN_DISABLE_ASSERT; // Whether the default 'assert' et al is disabled in code or not
 	bool   ODIN_DEFAULT_TO_NIL_ALLOCATOR; // Whether the default allocator is a "nil" allocator or not (i.e. it does nothing)
@@ -1537,6 +1538,12 @@ bool init_build_paths(String init_filename) {
 		enable_target_feature({}, bc->target_features_string);
 	}
 
+	{
+		String build_project_name  = last_path_element(bc->build_paths[BuildPath_Main_Package].basename);
+		GB_ASSERT(build_project_name.len > 0);
+		bc->ODIN_BUILD_PROJECT_NAME = build_project_name;
+	}
+
 	return true;
 }