Add build tests to verify correct compilation of as many modules as possible under as many architectures as possible.

Fix broken compilation of LUFA under C++ compilers when the Serial peripheral module header file is included in a C++ source file.

Fix missing semicolon in the UC3 architecture host pipe functions.

Fix failed compilation for the XMEGA architecture if USB_DEVICE_ONLY us not specified.

BuildTests/makefile

@@ -0,0 +1,19 @@
+#
+#             LUFA Library
+#     Copyright (C) Dean Camera, 2011.
+#
+#  dean [at] fourwalledcubicle [dot] com
+#           www.lufa-lib.org
+#
+
+# Makefile to build all the LUFA Build Tests. Build Tests are
+# used to verify the correctness of the LUFA library, and are
+# not intended to be modified or compiled by non-developers.
+
+all:
+	$(MAKE) -C ModuleTest clean
+	$(MAKE) -C ModuleTest all
+
+%:
+	$(MAKE) -C ModuleTest $@
+