libusbg: Add extern "C" linkage specification when using C++
libusbg: Add extern "C" linkage specification when using C++

This allows using libusbg in C++ code, without requiring users to
manually wrap the #include statement.

Signed-off-by: Dominic Sacré <dominic.sacre@gmx.de>

Add libusbg: to commit message.

Signed-off-by: Krzysztof Opasiak <8064eda6f94b3817252b7d7649cf754592f63500@samsung.com>

pszewczyk/libusbg,pszewczyk/libusbg